Patent Publication Number: US-10328944-B2

Title: Systems and methods for active engine mount diagnostics

Description:
FIELD 
     The present description relates generally to methods and systems for controlling a vehicle engine to induce vehicle vibrations to diagnose whether active engine mounts are functioning as desired. 
     BACKGROUND/SUMMARY 
     Engines historically have had solid rubber mounts to isolate engine vibration from the vehicle cabin and chassis, where the rubber naturally absorbed vibrations from the engine. However, in performance and high end cars, if rubber is too compliant, then certain vehicle maneuvers may cause high loads, and this may stress joints in the vehicle, for example in the exhaust system. Hence, tunable active engine mounts have been developed that may be controlled to change dampening characteristics depending on engine load. 
     As an example, the active engine mounts may be configured to be soft at engine idle to absorb undesired vibrations. However, at higher engine speeds, the active engine mounts may be configured to stiffen, to limit undesired engine motion, which may prevent stress on exhaust joints, for example. Accordingly, active engine mounts may achieve low noise, vibration, and harshness (NVH) at idle, and may further reduce NVH and prevent undesired stress at high loads. 
     For vehicles where a vehicle operator is typically operating the vehicle, the vehicle operator or other passengers in the vehicle may experience undesired NVH during certain vehicle conditions, which may result in the vehicle operator taking the vehicle to a repair shop such that a diagnosis can be made as to the source of the undesired NVH. However, there may be cases where a vehicle operator does not recognize the undesired NVH in a timely fashion to prevent vehicle complications arising from the undesired NVH. Furthermore, there may be instances, such as in the case of autonomously driven vehicles (AV), where a vehicle or passenger may not be present to observe undesired NVH. Thus, in such an example, as well as in examples where a vehicle operator may be present, it may be desirable to periodically conduct a diagnostic test as to whether the active engine mounts are functioning as desired. 
     The inventors herein have recognized these issues, and have developed systems and methods to at least partially address the above issues. In one example, a method is provided, comprising indicating degradation of an active engine mount by inducing degraded combustion events in a preselected engine cylinder, and operating the active engine mount in multiple modes, the indication responsive to an amount of vehicle chassis vibration during each of the modes. In this way, it may be periodically determined as to whether one or more active engine mounts in a vehicle are functioning as desired, such that NVH issues may be reduced. 
     As an example, the amount of vehicle chassis vibration is based on a level of fuel slosh in a fuel tank that provides fuel to the engine, where the level of fuel slosh is indicated via a fuel level sensor. In this way, the fuel level sensor may be utilized as a surrogate sensor for vehicle chassis vibration. 
     In one example, operating the active engine mount in multiple modes comprises commanding the active engine mount to a first, dampening mode of active engine mount operation for a first predetermined duration, followed by commanding the active engine mount to a second, stiffening mode of active engine mount operation for a second predetermined duration, and then commanding the active engine mount again to the first, dampening mode of active engine mount operation for a third predetermined duration. It may be understood that default operation of the active engine mount includes commanding the active engine mount to the first, dampening mode at idle conditions to absorb undesired chassis vibration, and commanding the active engine mount to the second, stiffening mode at higher engine speeds and loads to reduce undesired engine motion. 
     As an example, indicating degradation of the active engine mount may further comprise determining whether vibrations stemming from the vehicle chassis correlate with the degraded combustion events during controlling the active engine mounts to the first mode and the second mode. For example, it may be indicated that the active engine mount is functioning as desired responsive to vehicle chassis vibrations not correlating with degraded combustion events in the first mode, but where vehicle chassis vibrations are correlated with the degraded combustion events in the second mode. In another example, it may be indicated that the active engine mounts are stuck in the first mode responsive to vehicle chassis vibrations not correlating with the degraded combustion events in the first mode, and where vehicle chassis vibrations are not correlated with the degraded combustion events in the second mode. In yet another example, it may be indicated that the active engine mounts are stuck in the second mode responsive to vehicle chassis vibrations correlating with the degraded combustion events in the first mode, and where vehicle chassis vibrations are also correlated with the degraded combustion events in the second mode. 
     In an example, determining whether vibrations stemming from the vehicle chassis correlate with degraded combustion events during controlling the active engine mounts to the first mode and the second mode further comprises indicating that the vibrations stemming from the vehicle chassis correlate with the degraded combustion events responsive to the vibrations stemming from the vehicle chassis being above a threshold vibration level within a threshold time of the degraded combustion events. 
     As an example, inducing degraded combustion events in the preselected cylinder may comprise shutting off fueling to the preselected engine cylinder by commanding a fuel injector configured to provide fuel to the preselected engine cylinder to stop injection of fuel to the preselected engine cylinder. 
     In some examples, vehicle chassis vibration may be further increased by one or more of advancing spark in one or more remaining cylinders, the remaining cylinders comprising cylinders that do not comprise the preselected engine cylinder, via one or more spark plug(s) configured to provide spark to the one or more remaining cylinders. In another example, vehicle chassis vibration may be further increased by additionally or alternatively increasing and decreasing a speed of an engine of the vehicle in a cyclical fashion, turning on a compressor for an air conditioning system for a duration, and turning off the compressor for another duration in a cyclical fashion, and/or commanding an air intake throttle configured to enable air to be inducted into the engine, to a predetermined angle. 
     As yet another example, such a method may include commanding or maintaining application of one or more wheels brakes for one or more wheels of the vehicle, commanding or maintaining engaged an electronic parking brake for one or more wheels of the vehicle, and maintaining a vehicle transmission configurable to at least a park mode, a drive mode, and a reverse mode, in a drive mode of operation. 
     In this way, active engine mounts in a vehicle may be periodically assessed as to whether they are functioning as desired, whether or not the vehicle is occupied at the time of the active engine mount test diagnostic procedure. By periodically assessing the functionality of the active engine mounts, issues related to active engine mounts that are not functioning as desired, may be reduced or avoided. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically depicts an embodiment of a vehicle including a vehicle powertrain attached to a vehicle frame via one or more active engine mounts. 
         FIG. 2  shows an external view of an active engine mount that may be included within the vehicle of  FIG. 1 . 
         FIG. 3  shows a cross-sectional view of an example active engine mount, including a partitioning structure and decoupler element. 
         FIG. 4  schematically illustrates a block diagram of an example autonomous driving system. 
         FIG. 5  shows a high-level flowchart for an example method for conducting an active engine mount test diagnostic procedure. 
         FIG. 6  shows an example lookup table for diagnosing whether active engine mounts are functioning as desired, where the table is utilized as a part of the method depicted in  FIG. 5 . 
         FIG. 7  depicts an example timeline for conducting the active engine mount test diagnostic procedure, according to the method depicted in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for diagnosing whether active engine mounts in a vehicle are functioning as desired. For example, active engine mounts may be configured to isolate undesired noise, vibration, and harshness (NVH) from a vehicle chassis and cabin, as illustrated in the vehicle system depicted in  FIG. 1 . An example of an external view of an active engine mount, is depicted in  FIG. 2 . In some examples, an active engine mount may be controllable to at least two states, such as a first, dampening mode (e.g. idle mode), and a second, stiffening mode (e.g. ride mode). Accordingly, an example active engine mount controllable to a first, dampening mode, and a second, stiffening mode, is illustrated in  FIG. 3 . The vehicle system may in some examples comprise a vehicle propelled solely by an engine that combusts fuel (e.g. gasoline, diesel, or other fuel blend). However, in some examples, the vehicle system may comprise a hybrid vehicle, for example a hybrid electric vehicle (HEV), or a plug in hybrid electric vehicle (PHEV). In still other examples, the vehicle system may comprise an autonomously driven vehicle (AV). Accordingly,  FIG. 4  depicts an AV system that may be incorporated into the vehicle system of  FIG. 1 , to provide opportunities for autonomously driven modes of vehicle operation. The active engine mounts may periodically be diagnosed as to whether the active engine mounts are functioning as desired, according to the method depicted at  FIG. 5 . Conducting the active engine mount test diagnostic may in some examples include determining whether the active engine mounts are functioning as desired, whether the one or more active engine mounts are stuck in the dampening mode, or whether the one or more engine mounts are stuck in the stiffening mode. Thus, in some examples, a lookup table, as indicated at  FIG. 6 , may be utilized to diagnose the active engine mounts. A timeline for conducting an active engine mount test diagnostic procedure, according to the method of  FIG. 5 , is depicted at  FIG. 7 . 
     Turning now to  FIG. 1 , it schematically depicts an example vehicle system  100  as shown from a top view. Vehicle system  100  comprises a vehicle body  103  with a front end, labeled “FRONT”, and a back end labeled “BACK.” Vehicle system  100  may include a plurality of wheels  135 . For example, as shown in  FIG. 1 , vehicle system  100  may include a first pair of wheels adjacent to the front end of the vehicle and a second pair of wheels adjacent the back end of the vehicle. 
     Vehicle system  100  may include an internal combustion engine, such as example engine  10 , coupled to transmission  137 . Engine  10  and transmission  137  may herein be referred to in combination as a vehicle powertrain  110  or a powertrain  110 . It will be appreciated that other vehicle components coupled to one or more of engine and/or transmission  137  may also be included in the vehicle powertrain  110  without departing from the scope of the present invention. For example, engine  10  may include an engine intake  196  and an engine exhaust (not shown). Engine intake may include a throttle  197 , for controlling an amount of intake air to engine  10 . In some examples, throttle  197  may be controlled electronically via a controller, such as controller  12 . In other examples, throttle  197  may be mechanically coupled to an accelerator pedal  181 . 
     Vehicle system  100  is depicted as having a front wheel drive (FWD) transmission where engine  10  drives the front wheels via half shafts  109  and  111 . In another embodiment, vehicle system  100  may have a rear wheel drive (RWD) transmission which drives the rear wheels via a driveshaft (not shown) and a differential (not shown) located on rear axle  131 . In still other examples, vehicle system  100  may include a four wheel drive transmission. 
     Engine  10  and transmission  137  may be supported at least partially by frame, or chassis,  105 , which in turn may be supported by plurality of wheels  135 . As such, vibrations and movements from engine  10  and transmission  137  may be transmitted to frame  105 . Frame  105  may also provide support to a body of vehicle system  100  and other internal components such that vibrations from engine operation may be transferred to an interior, or cabin, of vehicle system  100 . In order to reduce transmission of vibrations to the interior, or cabin, of vehicle system  100 , engine  10  and transmission  137  may be mechanically coupled via a plurality of members  139  to respective active engine mounts  133 . Discussed herein, active engine mounts may refer to any type of active engine mount that may change its dampening characteristics. For example, such an active mount may be controlled to be relatively soft at engine idle to absorb undesired vibration, but may be controlled to stiffen at higher engine speeds and loads to limit undesired engine motion. As one example, engine manifold vacuum may be selectively applied to an active engine mount in order to change the characteristics of the active engine mount. Such an example will be discussed in greater detail with regard to  FIG. 3 . However, it may be understood that such an example is meant to be illustrative, and is not meant to be limiting. Thus, active engine mounts as discussed herein may refer to vacuum-regulated engine mounts, active motor mounts that counter engine vibration by commanding a counter shake to reduce intensity of engine vibration, magneto rheological mounts which may contain small particles of iron suspended in liquid such that when an electric current or magnetic field is applied to the fluid, the iron particles line up and effectively increase viscosity of the fluid, etc. 
     As depicted, engine  10  and transmission  137  are mechanically coupled at four locations to members  139  and via members  139  to four active engine mounts  133 . In other alternate embodiments, a different number of members and active engine mounts may be used, without departing from the scope of the present disclosure. 
     View  150  depicts a view of vehicle system  100  as observed from the front end of vehicle system  100 . Control system  15  including controller  12  may at least partially control engine  10  as well as vehicle system  100 . The controller  12  receives signals from the various sensors  13  of  FIG. 1  and employs the various actuators  81  of  FIG. 1  to adjust engine operation based on the received signals and instructions stored on a memory of the controller. As an example, vehicle system  100  may include sensors dedicated to indicating the occupancy-state of the vehicle, for example seat load cells  189 , door sensing technology  190 , and/or onboard cameras  191 . 
     In some examples control system  15  may be in communication with a remote engine start receiver  192  (or transceiver) that receives wireless signals  195  from a key fob  194  having a remote start button  193 . In other examples (not shown), a remote engine start may be initiated via a cellular telephone, or smartphone based system where a user&#39;s cellular telephone sends data to a server and the server communicates with the vehicle to start the engine. 
     Control system  15  and controller  12  may send control signals to actuators  81  which may include fuel injector  66  coupled to cylinder  30  in addition to other actuators of engine  10  and transmission  137  not depicted at  FIG. 1 . For illustrative purposes, only one cylinder  30  and one fuel injector  66  are shown. However, it may be understood that engine  10  may including a plurality of cylinders, and a plurality of fuel injectors. In some embodiments, each cylinder of engine  10  may include a spark plug  188  for initiating combustion. Control system  15  may provide an ignition spark to cylinder  30  via spark plug  188  in response to a spark advance signal from a controller, under select operating modes. However, in some embodiments, spark plug  188  may be omitted, such as where engine  10  may initiate combustion by auto-ignition or by injection of fuel as may be the case with some diesel engines. 
     Vehicle system  100  may include one or more fuel storage tanks  185  for storing fuel on-board the vehicle. For example, fuel tank  185  may store one or more liquid fuels, including but not limited to: gasoline, diesel, and alcohol fuels. In some examples, the fuel may be stored on-board the vehicle as a blend of two or more different fuels. For example, fuel tank  185  may be configured to store a blend of gasoline and ethanol (e.g., E10, E85, etc.) or a blend of gasoline and methanol (e.g., M10, M85, etc.), whereby these fuels or fuel blends may be delivered to engine  10 . Still other suitable fuels or fuel blends may be supplied to engine  10 , where they may be combusted at the engine to produce an engine output. The engine output may be utilized to propel the vehicle, for example. 
     In some embodiments, control system  15  may receive an indication of the level of fuel stored at fuel tank  185  via a fuel level sensor  187 , also referred to herein as fuel level indicator (FLI)  187 . The level of fuel stored at fuel tank  185  (e.g., as identified by the fuel level sensor  187 ) may be communicated to the vehicle operator, for example, via a fuel gauge or indication in a vehicle instrument panel (not shown). 
     Fuel tank  185  may be coupled to a fuel pump system  186 . The fuel pump system  186  may include one or more pumps for pressurizing fuel delivered to the injectors of engine  10 , such as the example injector  66  shown. As discussed, while only a single injector  66  is shown, additional injectors are provided for each cylinder. As depicted, fuel level sensor  187  may comprise a float connected to a variable resistor. Alternatively, other types of fuel level sensors may be used. 
     Controller  12  may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instruction or code programmed therein corresponding to one or more routines. In one example, engine  10  may be controlled at least partially by control system including controller  12  and by input from a vehicle operator  180 , or an autonomous controller (discussed in further detail below), via an input device  181 . In one example, input device  181  includes an accelerator pedal and a pedal position sensor  182  for generating a proportional pedal position signal PP. Similarly, control system  15  may receive an indication of an operator requested vehicle braking via a human operator  180 , or an autonomous controller. For example, control system  15  may receive sensory feedback from pedal position sensor  157  which communicates with brake pedal  156 . In some examples, vehicle system  100  may include an antilock brake system (ABS)  113 . The ABS may include wheel speed sensors  114 , for example. The ABS may further include at least two hydraulic valves (not shown) within the brake hydraulics (not shown). Controller  12  may monitor rotational speed of each wheel, and responsive to detection of a wheel rotating significantly slower than the others, the ABS  113  may be controlled to reduce hydraulic pressure to the brake  115  at the affected wheel, thus reducing the braking force on said wheel. Alternatively, responsive to detection of a wheel rotating significantly faster than the others, the ABS  113  may be controlled to increase hydraulic pressure to the brake at the affected wheel, thus increasing the braking force on said wheel. In still further cases, as will be discussed in detail below, ABS  113  may command an increased brake pressure at one or more wheels in order to conduct an active engine mount test diagnostic procedure. Herein, increasing brake pressure at one or more wheels via ABS  113  may be referred to as activating one or more wheel brakes. For example, ABS  113  may activate one or more wheel brakes in order to stiffen the vehicle frame and couple it mechanically to the engine, to conduct an active engine mount test diagnostic, as will be discussed in further detail below. 
     Vehicle system  100  may further include an air conditioning (A/C) system  199 , which may include an A/C compressor  198 . In some examples, the A/C compressor and A/C system may be electronically controlled via, for example, controller  12 . However, in other examples, A/C compressor  198  may be mechanically controlled, via, for example, being coupled to an engine crankshaft (not shown). 
     Vehicle system  100  may further include an electronic parking brake system  151 . Electronic parking brake system may be utilized in conjunction with the vehicle controller, to engage, or release, electronic parking brake(s)  152 , for example. 
     With regard to vehicle system  100 , noise, vibration, and harshness (NVH) may arise during engine operation, transmission operation, during transitions in engine operating modes, etc. Additionally, NVH may arise as a result of driving over rough (e.g., uneven) surfaces. Active engine mounts  133  may be designed to dampen vehicle noise and vibrations across a broad range of frequencies, or alternatively may be designed to dampen specific ranges of vibrational frequencies. In this way, NVH arising from a number of different sources may each be dampened by a common active engine mount  133 . 
     For example, as described above and which will be further elaborated below, active engine mounts  133  may be controlled via controller  12 , to a first configuration, or first mode, for idle operation, and to a second configuration, or mode, for operating at higher engine speeds and loads. As will be discussed in further detail below with regard to the method depicted at  FIG. 5 , an active engine mount test diagnostic procedure may be periodically conducted in order to ascertain whether the active engine mounts are functioning as desired. 
     Turning now to  FIG. 2 , an external view of an example active engine mount  200  is shown. It may be understood that such an example is meant to be illustrative, and is not meant to be limiting. Active engine mount  200  may be an example of active engine mount  133  shown within vehicle system  100  at  FIG. 1 . When configured in a vehicle system that is on flat ground (e.g., vehicle system  100  at  FIG. 1 ), active engine mount  200  may be oriented in a substantially vertical direction. However, in other configurations, active engine mount  200  may be oriented at an oblique angle relative to vertical. As used herein, however, the terms “upper” and “lower” may refer to respective ends of arrow  298 , which indicates a directional axis specific to the active engine mount. That is to say, arrow  298  provides reference for a relative positioning of components constituting active engine mount  200 , and not a reference for the orientation of active engine mount  200  within a vehicle system. Additionally, an upper end of the active engine mount may refer to the end closer toward the head of arrow  298  and a lower end of the active engine mount may refer the end closer toward the tail of arrow  298 . 
     Active engine mount  200  includes an upper external housing  202  with a central opening  212  formed within a top surface thereof. Upper external housing  202  may be formed from a rigid material, such as a metal or hard plastic. Central opening  212  is configured to receive a fastener or bolt  206 , which extends outwardly from a first elastomeric member or main rubber element (not shown, but see  FIG. 3 ) for fastening to a component of the vehicle powertrain (e.g., one of engine  10  at  FIG. 1 ). Bolt  206  may be formed from a rigid material such as steel or aluminum. 
     An upper end of bolt  206  may be configured to rotate about the clearance of central opening  212 , while the lower end (not shown) may be lodged in a first elastomeric member of the active engine mount, and as such the lower end of the bolt may remain relatively stationary compared to the upper end of the bolt. In another example, bolt  206  may extend outwardly from a bearing member (not shown) that is partially encapsulated within the first elastomeric member of the housing, and may be configured to transfer vibrations to the first elastomeric member via the bearing member. 
     Bolt  206  may be coupled to a rigid upper bracket  239  via a fastener  240 . It will be appreciated that upper bracket  239  may be similar to a member  139  described above with regard to  FIG. 1 . Upper bracket  239  may be formed from one of a metal or a hard plastic. A distal portion  238  of the upper bracket  239  may be coupled to a vehicle powertrain component (e.g., coupled to the powertrain component at a flange affixed thereto) via a fastener, in a manner generally known in the art. 
     Lower external housing  204  may be fastened (e.g., mechanically coupled) to upper housing  202 . Lower housing  204  may be formed from a rigid material such as one of a metal or hard plastic. A coupling of the lower housing to a vehicle frame (e.g.,  105  at  FIG. 1 ) may be achieved via a plurality of lower brackets. In this way, the external housing may remain structurally rigid (e.g., substantially non-compressible), and any vibrations absorbed from the vehicle powertrain or vehicle frame may be transferred to the first elastomeric member within the external housing, said first elastomeric member configured to dampen the vibrations. 
     Shown in  FIG. 2  are first lower bracket  232  and second lower bracket  234 . It will be appreciated that still further brackets may be affixed to lower housing  204  in a similar manner to brackets  232  and  234  without departing from the scope of the invention. The lower brackets may be formed from metal, such as steel. However, other materials may be used to form the lower brackets without departing from the scope of the present invention. First lower bracket  232  is shown integrally formed with lower housing  204 . A bolt (not shown) may couple (e.g., mechanically) lower bracket  232  to a vehicle frame via hole  282 . Second lower bracket  234  is shown affixed to, but not integrally formed with, lower housing  204 , and may similarly be coupled to the vehicle frame via hole  284 . 
       FIG. 3  shows a cross-sectional view  300  of an active engine mount (e.g., active engine mount  133  at  FIG. 1  or active engine mount  200  at  FIG. 2 ). It may be understood that the active engine mount depicted at  FIG. 3  is meant to be illustrative, and is not meant to be limiting. As used herein, the terms “upper” and “lower” may refer to respective ends of arrow  398 , as described above with reference to arrow  298  in  FIG. 2 . It will be appreciated that arrow  398  may provide a reference for the relative positioning of components within the active engine mount, as described above with reference to arrow  298 . 
     The active engine mount assembly may include an external housing  302  (e.g., similar to  202  at  FIG. 2 ) dimensioned to receive a first elastomeric member or main rubber element  304  that is generally shaped as a truncated cone, and primarily made of an elastomeric material, such as an elastic rubber as is conventional in the art. A bolt  306  (e.g., similar to  206  at  FIG. 2 ) extends outwardly from the first elastomeric member for fastening to the powertrain or engine (not shown, but see  FIG. 2 ) in a manner generally known in the art. In the depicted example, bolt  306  with a metal bearing member  308  of which at least a lower portion encapsulated within the first elastomeric member  304 . In addition, a lower peripheral portion of the first elastomeric member may include a stiffener, such as metallic stiffener  310 , molded within the first elastomeric member to add rigidity and support. In this way, vibrations and/or displacements from the powertrain may be transferred to the first elastomeric member  304  of the active engine mount. 
     As discussed above with regard to  FIG. 2 , the first elastomeric member is received within the upper external housing  302  so that the bolt  306  extends through a central opening  312  in the restrictor. The lower surface  305  of the first elastomeric member  304  forms a portion of a first or upper fluid chamber  316 , namely a high pressure side, of the engine mount. First fluid chamber  316  may be filled with a hydraulic fluid (e.g., glycol). The remainder of the first fluid chamber  316  is defined by the inertia track assembly  320 . It may be understood that inertia track assembly  320  may herein also be referred to as a partitioning structure. An outer portion of an upper surface of the partitioning structure (denoted by reference numeral  322 ) abuttingly and sealingly engages the first elastomeric member  304  in order to seal the first fluid chamber  316 . A second outer portion of the partitioning structure along the lower surface denoted by reference numeral  324  is sealingly engaged by a second elastomeric member  330  (a rubber boot or diaphragm) and particularly an upper peripheral portion  332  thereof. Lower surface  324  of the partitioning structure  320 , in combination with second elastomeric member  330 , form a second or lower fluid chamber  350 . Second fluid chamber may too be filled with a hydraulic fluid (e.g., glycol). The second elastomeric member  330  is protected by a diaphragm cover  334 , preferably formed of a more rigid material than the elastomeric diaphragm, and that matingly engages (e.g., mechanically couples to) the lower external housing  340 . When the lower housing  340  is fastened to the upper housing, the lower peripheral edge of the first elastomeric member  304  and the peripheral portion  332  of the second elastomeric member sealingly engage opposite sides or faces  322 ,  324 , respectively, of the partitioning structure  320 . 
     The partitioning structure and operation of a typical engine mount  300  will be briefly described. As indicated, the first fluid chamber  316  and the second fluid chamber  350  are fluidly coupled together by partitioning structure  320 . Partitioning structure  320  comprises a channel plate  301 , a decoupler  360  (e.g., compliant membrane), a first fluid track  370  (e.g., idle track), a second fluid track  440  (e.g. ride track), and a vacuum chamber  365 . Vacuum chamber  365  may be coupled to the partitioning structure such that the vacuum chamber may defined by passageways in the channel plate  301 , and wherein a segment of the vacuum chamber is defined by decoupler  360 . Vacuum chamber  365  may be fluidly connected to a source of either vacuum, or atmospheric pressure, via conduit  380 . Vacuum may be provided by any available source of vehicle vacuum, for example intake manifold vacuum. In one example, a first pressure  347  (e.g. atmospheric pressure), or a second pressure  348  (e.g. vacuum) may be applied to vacuum chamber  365 , via controlling two way valve  446 . For example, controller  12 , may command two way valve  446  to enable the first pressure, or the second pressure, to be communicated to vacuum chamber  365 , depending on vehicle operating conditions, as will be discussed in further detail below. More specifically, controller  12  may send a signal to two-way valve  346  to actuate the valve to either couple first pressure  347  to vacuum chamber  365 , or to couple second pressure  348  to vacuum chamber  365 . 
     When vacuum chamber  365  is at atmospheric pressure (e.g., a first pressure), decoupler  360  may be free to move. Furthermore, when vacuum chamber  365  is at atmospheric pressure, a first vacuum actuated valve  355  is seated in an upper position within channel plate  301  such that the first fluid track  370  is closed. When in such a configuration, the decoupler  360  may breathe in response to vibrations or displacements, and fluid flow between first fluid chamber  316  and second fluid chamber  350  may only be allowed via the second fluid track  375 . As such, engine mount  300  typifies decoupled engine mount function when vacuum chamber  365  is at atmospheric pressure. Such a configuration of active engine mount  300  may be termed a second, or stiffening mode of active engine mount operation. 
     Alternatively, application of vacuum to vacuum chamber  365  may serve to seat decoupler  360  against channel plate  301 , indicated by arrow  386 , and furthermore may position first vacuum actuated valve in a lower position, indicated by arrow  385 . As such, first fluid track  370  is opened, and decoupler  360  is not permitted to move, or breathe. Accordingly, fluid flow between first fluid chamber  316  and second fluid chamber  350  occurs via the first fluid track  370 , as first fluid track  370  represents the path of least resistance through the inertia track assembly  320 , thus providing a soft engine mount for idle mode operation. In other words, with vacuum chamber  365  coupled to second pressure  348  (e.g. vacuum), active engine mount  300  may be understood to be operating in a first, or dampening mode of active engine mount operation. 
     As discussed above, in some examples vehicle system  100  may be controlled autonomously, such that vehicle system  100  may be autonomously driven. In such an example, a vehicle operator and passengers may or may not be present in the vehicle during operation. In circumstances where a vehicle operator or passengers are not present, it may be challenging to diagnose whether undesired engine vibration is being transmitted to the vehicle frame and cabin. In such an example, the inventors herein find it desirable to periodically diagnose whether the active engine mounts are functioning as desired. However, it may be understood that such a diagnostic method, discussed in detail below with regard to  FIG. 5 , is not limited to use in vehicle that may be driven autonomously. 
       FIG. 4  is a block diagram of an example autonomous driving system  400  that may operate the vehicle system  100 , described above at  FIG. 1 . Herein, the vehicle system  100  will be referred to simply as a “vehicle”. The autonomous driving system  400 , as shown, includes a user interface device  410 , a navigation system  415 , at least one autonomous driving sensor  420 , and an autonomous mode controller  425 . 
     The user interface device  410  may be configured to present information to vehicle occupants, under conditions wherein a vehicle occupant may be present. However, it may be understood that the vehicle may be operated autonomously in the absence of vehicle occupants, under certain conditions. The presented information may include audible information or visual information. Moreover, the user interface device  410  may be configured to receive user inputs. Thus, the user interface device  410  may be located in the passenger compartment (not shown) of the vehicle. In some possible approaches, the user interface device  410  may include a touch-sensitive display screen. 
     The navigation system  415  may be configured to determine a current location of the vehicle using, for example, a Global Positioning System (GPS) receiver configured to triangulate the position of the vehicle relative to satellites or terrestrial based transmitter towers. The navigation system  415  may be further configured to develop routes from the current location to a selected destination, as well as display a map and present driving directions to the selected destination via, for example, the user interface device  410 . 
     The autonomous driving sensors  420  may include any number of devices configured to generate signals that help navigate the vehicle. Examples of autonomous driving sensors  420  may include a radar sensor, a lidar sensor, a vision sensor (e.g. a camera), vehicle to vehicle infrastructure networks, or the like. The autonomous driving sensors  420  may enable the vehicle to “see” the roadway and vehicle surroundings, and/or negotiate various obstacles while the vehicle  100  is operating in autonomous mode. The autonomous driving sensors  420  may be configured to output sensor signals to, for example, the autonomous mode controller  425 . 
     The autonomous mode controller  425  may be configured to control one or more subsystems  430  while the vehicle is operating in the autonomous mode. Examples of subsystems  430  that may be controlled by the autonomous mode controller  425  may include a brake subsystem, a suspension subsystem, a steering subsystem, and a powertrain subsystem. The autonomous mode controller  425  may control any one or more of these subsystems  430  by outputting signals to control units associated with subsystems  430 . In one example, the brake subsystem may comprise an anti-lock braking subsystem, configured to apply a braking force to one or more of wheels (e.g.  135 ). Discussed herein, applying the braking force to one or more of the vehicle wheels may be referred to as activating the brakes. To autonomously control the vehicle, the autonomous mode controller  425  may output appropriate commands to the subsystems  430 . The commands may cause the subsystems to operate in accordance with the driving characteristics associated with the selected driving mode. For example, driving characteristics may include how aggressively the vehicle accelerates and decelerates, how much space the vehicle leaves behind a front vehicle, how frequently the autonomous vehicle changes lanes, etc. 
     Turning to  FIG. 5 , a high-level example method  500  for conducting an engine mount diagnostic, is shown. Method  500  will be described with reference to the systems described herein and shown in  FIGS. 1-4 , though it should be understood that similar methods may be applied to other systems without departing from the scope of this disclosure. Method  500  may be carried out by a controller, such as controller  12  in  FIG. 1 , and may be stored at the controller as executable instructions in non-transitory memory. Instructions for carrying out method  500  may be executed by the controller based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference to  FIG. 1  and  FIG. 4 . The controller may employ vehicle system actuators, such as fuel injectors (e.g.  66 ), spark plug (e.g.  188 ), two way valve (e.g.  346 ), transmission (e.g.  137 ), brake pedal (e.g.  156 ), throttle (e.g.  197 ), electronic parking brake (e.g.  152 ), A/C compressor (e.g.  198 ), etc., according to the method depicted below. 
     Method  500  begins at  505 , and may include evaluating current operating conditions. Operating conditions may be estimated, measured, and/or inferred, and may include one or more vehicle conditions, such as vehicle speed, vehicle location, etc., various engine conditions, such as engine status, engine load, engine speed, A/F ratio, etc., various fuel system conditions, such as fuel level, fuel type, fuel temperature, etc., various evaporative emissions system conditions, such as fuel vapor canister load, fuel tank pressure, etc., as well as various ambient conditions, such as ambient temperature, humidity, barometric pressure, etc. 
     Proceeding to  510 , method  500  may include indicating whether conditions are met for conducting an active engine mount diagnostic procedure. For example, conditions being met may include an engine on condition. Conditions being met for the active engine mount diagnostic may further include an indication that the vehicle is in an idle mode, where the engine is running, but where the vehicle is not in motion. In other words, conditions being met for the active engine mount diagnostic may include static vehicle conditions. Still further, conditions being met for the active engine mount diagnostic may include a predetermined period of time elapsing since a prior active engine mount diagnostic procedure was conducted. In some examples, the predetermined period of time may include 30 days, or less than 30 days. In other examples, the predetermined period of time may include greater than 30 days, but less than 60 days. In further examples the predetermined period of time may include greater than 60 days. Such examples are meant to be illustrative, and are not meant to be limiting. 
     Conditions being met for the active engine mount diagnostic may, in some examples, additionally or alternatively include an indication of a remote start event. For example, a vehicle operator may initiate a remote start event via a key fob (e.g.  194 ), which may send a wireless signal (e.g.  195 ) to a remote engine start receiver (e.g.  192 ), to initiate engine activation, such that the engine begins combustion of air and fuel. 
     In some examples, conditions being met for the active engine mount diagnostic may additionally or alternatively include an indication that the vehicle is not occupied. For example, the vehicle controller (e.g.  12 ) may interpret signals received from seat load cells (e.g.  189 ), door sensing technology (e.g.  190 ), and/or onboard camera(s) (e.g.  191 ), to determine whether the vehicle is occupied. In some examples, method  500  may include prohibiting, or aborting an active engine mount diagnostic if the vehicle is indicated to be occupied. Furthermore, while not explicitly illustrated at  FIG. 5 , it may be understood that in some examples, responsive to an active engine mount diagnostic commencing, such a diagnostic may be aborted if it is indicated that the vehicle has become occupied while the diagnostic is in progress. Still further, it may be understood that, in some examples, the active engine mount diagnostic may be conducted even if it is indicated that the vehicle is occupied. 
     If, at  510 , conditions are not indicated to be met for the active engine mount diagnostic procedure, method  500  may proceed to  515 , and may include maintaining current vehicle operating conditions without conducting the active engine mount diagnostic procedure. Method  500  may then end. 
     Returning to  510 , if conditions are indicated to be met for conducting the active engine mount diagnostic procedure, method  500  may proceed to  520 . At  520 , method  500  may include commanding the transmission (e.g.  137 ) to “drive”. More specifically, vehicle transmission may be configured in one of park, reverse, neutral, drive, or low, for example. Thus, at  520 , method  500  may include commanding the transmission to the drive mode of operation, or if already in drive mode, maintaining the transmission in drive mode. Furthermore, at step  520 , method  500  may include activating wheel brakes via, for example, antilock braking system (e.g.  113 ) configured to increase hydraulic pressure to one or more vehicle wheels to increase braking force on the one or more wheels. In one example, where the brake pedal is already depressed via a vehicle operator, the brake pedal may be maintained depressed. With the vehicle transmission configured in drive mode, and with the brake pedal depressed, or with brakes activated, the vehicle frame (e.g.  105 ) may be stiffened, and mechanically coupled to the engine (e.g.  10 ). In some examples, at  520 , method  500  may further include the vehicle controller communicating with (e.g. sending a signal to), an electronic parking brake system (e.g.  151 ), to engage an electronic parking brake (e.g.  152 ). Engaging the electronic parking brake at step  520  may serve to further mechanically couple the vehicle frame (e.g.  105 ), to the engine (e.g.  10 ). 
     Proceeding to  525 , method  500  may include inducing vehicle vibration. As an example, at  525 , method  500  may include cutting off fueling to a preselected engine cylinder (e.g.  30 ). For example, the vehicle controller may send a command to a fuel injector (e.g.  66 ), actuating the fuel injector to stop injection of fuel to the preselected engine cylinder. In one example, the preselected engine cylinder may include a cylinder that, when fuel injection is terminated to that cylinder, results in the greatest amount of vibration being transmitted to the vehicle frame. In other words, degraded combustion may be induced in the preselected cylinder such that engine mechanical vibration, the result of degraded combustion while fuel injection to the preselected cylinder is stopped, is transmitted to the vehicle frame in a predictable fashion. More specifically, vibrations from the engine and transferred to the vehicle frame may correspond to the degraded combustion events, such that degraded combustion events may be correlated with increased vibration, as will be elaborated upon in more detail below. 
     In some examples, at  525 , method  500  may additionally or alternatively include commanding an electronically-controlled throttle (e.g.  197 ) to a wider angle, or more open position. In other words, the vehicle controller (e.g.  12 ) may send a signal to an actuator of the electronic throttle, actuating the throttle to a more open position, such that more intake air may be routed to the engine for combustion. 
     In some examples, at  525 , method  500  may additionally or alternatively include advancing spark in the cylinder(s) that have not been cut off from fuel injection. For example, as discussed above, a preselected cylinder may be cut off from fuel injection at  525 . Thus, the cylinders that do not comprise the preselected cylinder may be spark advanced, to create engine knock, which may further increase engine vibrations. Specifically, the vehicle controller (e.g.  12 ) may send a signal to a spark plug (e.g.  188 ), actuating the spark plug to advance combustion initiation. 
     In some examples, at  525 , method  500  may additionally or alternatively include “revving” the engine up and down in a periodic fashion. More specifically, the vehicle controller (e.g.  12 ) may regulate engine speed (RPM) to increase to a first predetermined RPM, then decrease to a second predetermined RPM, in a sequence that may repeat for the duration of the active engine mount test diagnostic. By revving the engine speed up and down in periodic fashion throughout the duration of the active engine mount test diagnostic, vehicle vibration may be increased. 
     Still further, in some examples, at  525  method  500  may additionally or alternatively include turning on and off a compressor (e.g.  198 ) for an A/C system (e.g.  199 ). For example, the A/C compressor may be turned on for a first predetermined duration, then turned off for a second predetermined duration. Such a procedure may repeat for the duration of the active engine mount test diagnostic procedure, for example. By cycling on and off the A/C compressor, vehicle vibration may be increased. 
     Proceeding to  530 , method  500  may include commanding active engine mounts to a first mode (e.g. dampening mode) of operation, and may further include recording the resulting pattern of vehicle frame vibration. In one example, referring to the example active engine mount (e.g.  300 ) depicted at  FIG. 3 , commanding the active engine mounts to the first, dampening mode of operation may include commanding a two-way valve (e.g.  346 ) to couple vacuum (e.g.  348 ) to a vacuum chamber (e.g.  365 ) of the active engine mount (e.g.  300 ). In one example, vibration may be monitored via a fuel level sensor, or fuel level indicator (e.g.  187 ), positioned within the fuel tank. More specifically, vehicular vibration may be monitored as a function of fuel slosh in a fuel tank (e.g.  185 ), where fuel slosh may be determined via the fuel level sensor, or fuel level indicator. For example, as fluctuations in fuel level increase, as monitored via the fuel level sensor, it may be indicated that vehicle vibrations are increasing. Similarly, as fluctuations in fuel level decrease, as monitored via the fuel level sensor, it may be indicated that vehicle vibrations are decreasing. In other words, greater fuel slosh, as indicated via fuel level fluctuations, may indicate greater vehicle vibration, whereas lesser fuel slosh, as indicate via fuel level fluctuations, may indicate lesser vehicle vibration. 
     Herein, the first mode of active engine mount operation may be understood to include a damping mode of operation. In the damping mode, vehicle vibrations due to the degraded combustion events may be expected to be dampened via the active engine mounts, such that little to no vibrations may be indicated responsive to the degraded combustion events. In other words, in the damping, or first mode, vehicle vibrations may not be expected to correlate with the degraded combustion events. Instead, the mechanical vibrations induced by the degraded combustion events may be effectively damped via the active engine mounts, such that little to no vibration is indicated as monitored via the vibrational, or inertial, sensors. It may be understood that the greatest source of vehicle vibration may stem from the degraded combustion events, and that any additional methodology of increasing vehicle vibration (e.g. advancing spark, cycling the A/C compressor on and off, cyclically revving the engine, etc.), may serve to further increase the vibrations induced by degraded combustion events. As such, correlating vibrations as monitored via the fuel level sensor (e.g.  187 ) with degraded combustion events may provide a robust means for analyzing the effectiveness of vehicle active engine mounts. Vibrations that are effectively dampened may herein refer to vibrations that are below a vibration threshold, for example. 
     Commanding the active engine mounts to the first mode at  530  may include commanding the active engine mounts to the first mode for a first predetermined time duration. Accordingly, proceeding to  535 , method  500  may include indicating whether the first predetermined time duration has elapsed. If the first predetermined time duration is not yet indicated to have elapsed, method  500  may return to  530 , and may include continuing to maintain the active engine mounts in the first mode, and may further include continuing to record the resulting pattern of vehicle frame vibration via the fuel level indicator (e.g.  187 ). 
     Alternatively, responsive to the first predetermined time duration elapsing at  535 , method  500  may proceed to  540 . At  540 , method  500  may include commanding the active engine mounts to a second mode of operation, and may further include recording the resulting pattern of vehicle frame vibration. Referring to the example active engine mount (e.g.  300 ) depicted at  FIG. 3 , commanding the active engine mount to the second mode of operation may include commanding a two-way valve (e.g.  346 ) to couple atmospheric pressure (e.g.  347 ) to a vacuum chamber (e.g.  365 ) of the active engine mount. Similar to that discussed above, vibration may be monitored via a fuel level indicator (e.g.  187 ). Herein, the second mode of active engine mount operation may be understood to include a stiffening mode of operation. In the stiffening mode, vehicle vibrations due to the degraded combustion events (and further responsive to additional vehicle vibration induced via advancing spark, cyclically revving engine speed, cycling the A/C compressor on and off, etc.) may be expected to be significant, or not substantially dampened, such that vehicle vibrations as recorded via the fuel level indicator, may be correlated with the degraded combustion events. As discussed, the resulting pattern of vehicle vibration while the predetermined cylinder is cut off from fuel injection, and while the active engine mounts are configured in the second mode (e.g. stiffening mode), may be stored at the controller. Herein, vehicle vibrations not effectively dampened may refer to vehicle vibrations that are above the vibration threshold, for example, as compared to vehicle vibrations that are effectively dampened, which may be below the vibration threshold. 
     Commanding the active engine mounts to the second mode at  540  may include commanding the active engine mounts to the second mode for a second predetermined time duration. In some examples, the second predetermined time duration may be different than that of the first predetermined time duration. However, in other examples, the second predetermined duration may comprise the same, or substantially the same, time duration as the first predetermined time duration. Accordingly, proceeding to  545 , method  500  may include indicating whether the second predetermined time duration has elapsed. If, at  545 , the second predetermined time duration is not yet indicated to have elapsed, method  500  may return to  540 , and may include continuing to maintain the active engine mounts in the second mode, and may further include continuing to record the resulting pattern of vehicle frame vibration. 
     Alternatively, responsive to the second predetermined time duration elapsing at  545 , method  500  may proceed to  550 . At  550 , method  500  may include commanding the active engine mounts to the first mode of operation again. As discussed above, the first mode of operation may include a mode of operation wherein the active engine mounts are configured in a damping mode of operation. Accordingly, the resulting pattern of vehicle frame vibration may again be recorded via the vehicle controller while the active engine mounts are configured in the first mode. The return to the first mode of operation may be carried out for a third predetermined time duration. In some examples, the third predetermined time duration may be the same, or substantially the same, as the first predetermined time duration and/or the second predetermined time duration. However, in other examples, the third predetermined time duration may not be the same time duration as that of the first predetermined time duration, or the second predetermined time duration. 
     Thus, proceeding to  555 , method  500  may include indicating whether the third predetermined time duration has elapsed. If, at  555 , the third predetermined time duration is not yet indicated to have elapsed, method  500  may return to  550 , and may include continuing to maintain the active engine mounts in the first mode, and may further include continuing to record the resulting pattern of vehicle frame vibration. 
     Alternatively, responsive to the third predetermined time duration elapsing at  555 , method  500  may proceed to  560 . At  560 , method  500  may include conducting an active engine mount diagnosis according to the table depicted at  FIG. 6 . 
     Turning now to  FIG. 6 , table  600  illustrates potential outcomes of the active engine mount test diagnostic procedure. In some examples, table  600  may comprise a lookup table, and may be stored at the vehicle controller, for example. The recorded pattern of vehicle vibration during the first predetermined time period where the active engine mounts are configured in the first mode, during the second predetermined time period where the active engine mounts are configured in the second mode, and during the third predetermined time period where the active engine mounts are configured in the first mode, may be compared to table  600  in order to diagnose the active engine mounts. 
     Three potential diagnoses are indicated, termed outcome A, outcome B, and outcome C. More specifically, it may be determined as to whether vehicle frame vibrations are correlated with degraded combustion events. In some examples, vehicle vibrations may be correlated with degraded combustion events responsive to indicated vehicle vibration(s) above a threshold vibration level (vibration threshold level), as discussed above, and may further comprise the vehicle vibration(s) within a threshold time of the degraded combustion event. For example, a magnitude of vehicle frame vibrations may be indicated via the fuel level indicator (e.g.  187 ), and the magnitude of the vibrations may be compared to the threshold vibration level. Furthermore, a timing sequence of degraded combustion events may be stored at the controller, and vehicle vibrations that are above the threshold vibration level, and which are within a threshold time of the degraded combustion event, may be indicated to be correlated with a particular degraded combustion event. Based on the mode of operation of the active engine mounts in the first predetermined time period  530 , the second predetermined time period  540 , and the third predetermined time period  550 , and whether the vibrational pattern of the vehicle frame is correlated with degraded combustion events during the first, second, and third predetermined time period, a diagnosis may be determined as to whether the active engine mounts are functioning as desired (e.g. outcome A), whether active engine mounts are stuck in the first, damping mode (e.g. outcome B), or whether the active engine mounts are stuck in the second, stiffening mode (e.g. outcome C). 
     More specifically, it may be determined that the vehicle active engine mounts are functioning as desired (e.g. outcome A) responsive to the recorded vibrational pattern not correlating (No) with degraded combustion events in the first mode during the first predetermined time period, correlating (yes) with degraded combustion events in the second mode during the second predetermined time period, and not correlating (No) with degraded combustion events in the first mode during the third predetermined time period. As an example, during the first predetermined time period where the active engine mounts are configured in the first mode, degraded combustion events may be expected to be substantially dampened. Thus, the recorded pattern of vibration may not be expected to correlate with degraded combustion events. In other words, any vibrations induced by the degraded combustion events may be expected to be below the threshold vibration level. Alternatively, responsive to the active engine mounts being configured in the second position during the second predetermined time period, vibrations induced by the degraded combustion events may be expected to be above the threshold vibration level, thus the recorded vibrational pattern may be expected to correlate with the degraded combustion events during the second predetermined time period, where the active engine mounts are configured in the second position. Furthermore, during the third predetermined time period, where the active engine mounts may be returned to the first, dampening mode of operation, it may be again expected that the recorded pattern of vibration may not correlate with degraded combustion events. 
     Thus, if a recorded pattern of vehicle frame vibration does not correlate (No) with degraded combustion events in the first mode during the first predetermined time duration, correlates (Yes) with degraded combustion events in the second mode during the second predetermined time duration, and does not correlate (No) with degraded combustion events in the first mode during the third predetermined time duration, it may be indicated that the active engine mounts are functioning as desired. 
     In another example, it may be determined that the vehicle active engine mounts are stuck in the first, dampening mode (e.g. outcome B), responsive to the recorded vibrational pattern not correlating (No) with degraded combustion events in the first mode during the first predetermined time period, not correlating (No) with degraded combustion events in the second mode during the second predetermined time period, and not correlating (No) with degraded combustion events in the first mode during the third predetermined time period. As discussed above, during the first predetermined time period where the active engine mounts are configured in the first mode, degraded combustion events may be expected to be substantially dampened, which is observed during the first predetermined time period, as the vibrational pattern is not indicated to be correlated with degraded combustion events (No). Upon transition to the second mode of operation during the second predetermined time period, it may be expected that the recorded pattern of vibrations correlate with degraded combustion events. However, for outcome B, upon transition to the second mode of operation, the pattern of vehicle vibrations are not indicated to be correlated with degraded combustion events. Furthermore, during the third predetermined time period where the active engine mounts are configured again in the first mode, degraded combustion events may be expected to be substantially dampened. Thus, responsive to the recorded vibrational pattern not correlating with degraded combustion events during any of the first predetermined time duration where the active engine mounts are configured in the first mode, second predetermined time duration where the active engine mounts are configured in the second mode, and third predetermined time duration where the active engine mounts are configured in the first mode, it may be indicated that the active engine mounts may be stuck in the first, dampening mode of operation (e.g. outcome B). 
     In another example, it may be determined that the vehicle active engine mounts are stuck in the second, stiffening mode (e.g. outcome C), responsive to the recorded vibrational pattern correlating (Yes) with degraded combustion events in the first mode during the first predetermined time period, correlating (Yes) with degraded combustion events in the second mode during the second predetermined time period, and further correlating (Yes) with degraded combustion events in the first mode during the third predetermined time period. As discussed above, during the first predetermined time period where the active engine mounts are configured in the first mode, degraded combustion events may be expected to be substantially dampened, which may not be observed during the first predetermined time period for outcome C. In other words, while the vehicle frame vibrations are not expected to be correlated with the degraded combustion events during the first predetermined time period, instead, the vehicle frame vibrations are indicated to be correlated (Yes) with the degraded combustion events. Furthermore, upon transition to the second mode of operation during the second predetermined time period, it may be expected that the recorded pattern of vibrations correlate with degraded combustion events. For outcome C, the recorded pattern of vibrations is indicated to correlate (Yes) with degraded combustion events during the second predetermined time period where the active engine mounts are configured in the second mode. Still further, upon transition to the first mode of operation during the third predetermined time period, it may be expected that the recorded pattern of vibrations do not correlate with degraded combustion events. However, for outcome C, the recorded pattern of vibrations is indicated to correlate (Yes) with degraded combustion events during the third predetermined time period where the active engine mounts are configured in the first mode. Thus, responsive to the recorded vibrational pattern correlating (Yes) with degraded combustion events during each of the first predetermined time duration where the active engine mounts are configured in the first mode, the second predetermined time duration where the active engine mounts are configured in the second mode, and the third predetermined time duration where the active engine mounts are configured in the first mode, it may be indicated that the active engine mounts may be stuck in the second, stiffening mode of operation (e.g. outcome C). 
     Thus, returning to step  560  of method  500 , the method may include diagnosing whether the active engine mounts are functioning as desired (e.g. outcome A), whether the active engine mounts are stuck in the first mode (e.g. outcome B), or whether the active engine mounts are stuck in the second mode (e.g. outcome C). As discussed, the pattern of vehicle frame vibration during the first, second, and third predetermined time durations may be determined, and it may be further indicated as to whether such patterns correlate with degraded combustion events during each of the first, second, and third predetermined time durations. By comparing the results of whether vehicle vibrations are correlated with degraded combustion events during the first predetermined time period where the active engine mounts are configured in the first mode, during the second predetermined time period where the active engine mounts are configured in the second mode, and during the third predetermined time period where the active engine mounts are configured in the first mode, table  600  may be used to diagnose functionality of the active engine mounts. 
     Accordingly, proceeding to  565 , method  500  may include indicating whether the active engine mounts are functioning as desired, or whether the active engine mounts are stuck in either the first, dampening mode, or the second, stiffening mode. Responsive to an indication that the active engine mounts are functioning as desired, method  500  may proceed to  575 , and may include updating vehicle operating parameters. Updating vehicle operating parameters at  575  may include storing the results of the test diagnostic at the controller. For example, it may be indicated that an active engine mount diagnostic was conducted, and that responsive to the active engine mount diagnostic being conducted, it was determined that the vehicle active engine mounts are functioning as desired. 
     At  575 , it may be further understood that vehicle operating conditions may be returned to default operating conditions. For example, active engine mounts (e.g.  133 ) may be returned to a default operating condition. In some examples, default operating condition may comprise the first, dampening mode, while in other examples, default operating conditions may comprise the second, stiffening mode. Furthermore, the engine speed may be returned to a default engine speed, which may comprise an engine idle speed, for example. Still further, a throttle position may be returned to a default throttle position. Such a default throttle position may comprise a throttle position less opened (less of a wide angle) than the throttle position during the test diagnostic. Still further, the A/C compressor may stop being cycled on an off, under conditions where the A/C compressor was cycled on and off during the test diagnostic. Still further, fuel may again be injected into the preselected cylinder, and spark to the non-preselected cylinders may be returned to default spark timing (e.g. not advanced). Still further, the brakes (e.g. brake pedal and electronic parking brake) may be returned to default status, which may include a status prior to the commencement of the test diagnostic procedure. Still further, the transmission may be returned to a default state, which may comprise a state of the transmission prior to commencement of the test diagnostic procedure. Method  500  may then end. 
     Alternatively, at  565 , responsive to an indication that the active engine mounts are not functioning as desired, method  500  may proceed to  570 . For example, at  570 , method  500  may include indicating that either the active engine mounts are stuck in the first, dampening mode, or that the active engine mounts are stuck in the second, stiffening mode. Accordingly, at  570 , method  500  may include updating vehicle operating parameters. For example, updating vehicle operating parameters at  570  may include storing the results of the test diagnostic at the controller. More specifically, it may be indicated that an active engine mount test diagnostic procedure was conducted, and that responsive to the active engine mount being conducted, the active engine mounts are indicated to be stuck in one of the first mode, or the second mode, depending on the outcome of the test diagnostic. Updating vehicle operating parameters at  570  may further include setting a flag at the controller, or setting a diagnostic trouble code (DTC). Still further, updating vehicle operating parameters at  570  may include illuminating a malfunction indicator light (MIL), alerting a vehicle operator (if present) of the need to service the vehicle. In some examples, updating vehicle operating parameters at  570  may include limiting a maximum engine speed responsive to an indication that the active engine mounts are stuck in the second, stiffening mode. 
     At  570 , it may be further understood that vehicle operating conditions may be returned to default operating conditions. For example, active engine mounts (e.g.  133 ) may be returned to a default operating condition. In some examples, default operating condition may comprise the first, dampening mode, while in other examples, default operating conditions may comprise the second, stiffening mode. Furthermore, the engine speed may be returned to a default engine speed, which may comprise an engine idle speed, for example. Still further, a throttle position may be returned to a default throttle position. Such a default throttle position may comprise a throttle position less opened (less of a wide angle) than the throttle position during the test diagnostic. Still further, the A/C compressor may stop being cycled on an off, under conditions where the A/C compressor was cycled on and off during the test diagnostic. Still further, fuel may again be injected into the preselected cylinder, and spark to the non-preselected cylinders may be returned to default spark timing (e.g. not advanced). Still further, the brakes (e.g. brake pedal and electronic parking brake) may be returned to default status, which may include a status prior to the commencement of the test diagnostic procedure. Still further, the transmission may be returned to a default state, which may comprise a state of the transmission prior to commencement of the test diagnostic procedure. Method  500  may then end. 
     Turning now to  FIG. 7 , an example timeline  700  is shown, for conducting an active engine mount test diagnostic procedure, according to method  500  depicted herein, and with reference to  FIG. 5 , and as applied to the systems described herein and with reference to  FIGS. 1-4 . Timeline  700  includes plot  705 , indicating whether a vehicle engine (e.g.  10 ) is in operation (yes), or not (no), over time. For example, an engine in operation may include the engine combusting air and fuel. Timeline  700  further includes plot  710 , indicating vehicle speed, over time. The vehicle may be stopped, or may be traveling at various speeds (+) greater than when stopped. Timeline  700  further includes plot  715 , indicating whether conditions are met for an engine mount test, over time. Conditions may be met (yes), or not (no). Timeline  700  further includes plot  720 , indicating whether the active engine mounts are configured in a first, dampening mode, or a second, stiffening mode, over time. Timeline  700  further includes plot  725 , indicating whether fueling to a preselected cylinder is maintained (on), or cut off (off), over time. Timeline  700  further includes plot  730 , indicating whether degraded combustion events are indicated (yes), or not (no), over time. Timeline  700  further includes plot  735 , indicating vibrations of the vehicle frame as recorded via a fuel level indicator (FLI), over time. Vibrations as indicated by fuel level slosh, may increase (+), or decrease (−), for example. Line  736  represents a threshold vibration level, above which vehicle frame vibrations may be correlated with degraded combustion events. Timeline  700  further includes plot  740 , indicating whether the active engine mounts are functioning as desired (yes), or not (no), over time. Timeline  700  further includes plot  745 , indicating an engine RPM, over time. Engine RPM may increase (+), or decrease (−), for example. 
     At time t 0 , the engine is indicated to be in operation indicated by plot  705 , and thus may be understood to be combusting air and fuel. The vehicle is traveling above a stopped speed, indicated by plot  710 . However, conditions are not indicated to be met for conducting an active engine mount diagnostic test procedure, indicated by plot  715 . As discussed above, conditions being met may include an engine idle mode, where the engine is on but where the vehicle is not in motion, a static condition, a predetermined period of time elapsing since a prior active engine mount diagnostic procedure, an indication of a remote start event, an indication that the vehicle is not occupied, etc. As conditions are not indicated to be met for the active engine mount test diagnostic, fueling to the preselected cylinder is maintained, indicated by plot  725 . Accordingly, no degraded combustion events are indicated, illustrated by plot  730 . Furthermore, the active engine mounts are configured in the first, damping mode of operation, indicated by plot  720 . Thus, the fuel level indicator indicates a low level of vibration from the vehicle frame, indicated by plot  735 . Still further, at time t 0 , the active engine mounts are indicated to be functioning as desired. Although the engine mounts may not, in fact be functioning as desired, as will be discussed in more detail below, at time t 0 , the engine mounts are indicated to be functioning as desired. For example, an active engine mount test diagnostic may not have been conducted since a prior engine mount test diagnostic where the active engine mounts were indicated to be functioning as desired. Thus, at time t 0 , the active engine mounts are indicated to be functioning as desired. 
     Between time t 0  and t 1 , the vehicle slows down and comes to a stop with the engine maintained running. Furthermore, at time t 1 , conditions are indicated to be met for conducting the active engine mount test diagnostic procedure. While not explicitly illustrated, it may be understood that responsive to conditions being met for the active engine mount test diagnostic, a brake pedal (e.g.  156 ) may be maintained depressed, or wheel brakes may be commanded via the controller to an activated state, where braking force to one or more wheels may be increased. Still further, the vehicle transmission (e.g.  137 ) may be maintained in drive, or commanded via the controller to drive. Still further, an electric parking brake (e.g.  152 ) may be commanded via the vehicle controller to be engaged. Accordingly, at time t 1 , fueling is cut off to the preselected engine cylinder. More specifically, a command may be sent from the controller to a fuel injector (e.g.  66 ) configured to deliver fuel to the preselected cylinder, commanding the fuel injector be stopped from delivering fuel to the preselected cylinder. By cutting off fuel injection to the preselected cylinder, degraded combustion events may be induced. Furthermore, engine RPM is commenced cycling between an increased RPM, and a decreased RPM. For example, engine RPM may be increased to a first predetermined RPM, and then decreased to a second predetermined RPM, and such a cycle may be continued throughout the duration of the active engine mount test diagnostic, indicated by plot  745 . 
     Still further, while not explicitly illustrated, in some examples it may be understood that, responsive to conditions being met for the active engine mount test diagnostic, spark to the engine cylinders not comprising the preselected cylinder may be advanced, to increase vehicle vibration. In yet another example, responsive to conditions being met for the active engine mount test diagnostic, a throttle may be commanded via the vehicle controller to a more opened, or widened, position. Such an increased opening of the throttle may result in greater intake air flow to the engine, for example, which may increase vehicle vibration. In still another example, responsive to conditions being met for the active engine mount test diagnostic, an A/C compressor may be turned on and off in a cyclical fashion for the duration of the active engine mount test diagnostic procedure. As discussed above, the A/C compressor may be commanded via the vehicle controller to an “on” configuration for a first predetermined time period, then turned “off” for a second predetermined time period. It may be understood that the A/C compressor may be cycled on and off in such a fashion for the duration of the active engine mount test diagnostic. 
     Thus, between time t 2  and t 3 , with the active engine mounts configured in the first, damping mode, vehicle frame vibrations, for example a pattern of vehicle frame vibrations, are recorded. As indicated, three degraded combustion events are indicated between time t 2  and t 3 , however, such an example is illustrative, and more than three degraded combustion events may occur between time t 2  and t 3 . The time period between time t 2  and t 3  may be understood to comprise the first predetermined time period, as discussed above. 
     At time t 3 , the active engine mounts are switched from the first mode, to the second, stiffening mode. Between time t 3  and t 4 , with the active engine mounts configured in the second mode, the pattern of vehicle frame vibrations are recorded by the vehicle controller. Similar to that described above, three degraded combustion events are indicated between time t 3  and t 4  however there may be more than three degraded combustion events between time t 3  and t 4 . The time period between time t 3  and t 4  may be understood to comprise the second predetermined time period, as discussed above. 
     At time t 4 , the active engine mounts are switched from the second mode, back to the first mode. Between time t 4  and t 5 , with the active engine mounts configured in the second mode, the pattern of vehicle frame vibrations are recorded by the vehicle controller. Similar to that described above, three degraded combustion events are indicated between time t 4  and t 5  however there may be more than three degraded combustion events between time t 4  and t 5 . The time period between time t 4  and t 5  may be understood to comprise the third predetermined time period, as discussed above. 
     Between time t 2  and t 5 , plot  740  is indicated as a dotted line in order to illustrate that the active engine mount test diagnostic procedure is underway, and thus, it is unknown as to whether the active engine mounts are functioning as desired during the time period between time t 2  and t 5 . 
     At time t 5 , the active engine mount test diagnostic procedure is complete. In other words, vehicle vibrations have been recorded during the first predetermined time period with the active engine mounts in the first mode, during the second predetermined time period with the active engine mounts in the second mode, and during the third predetermined time period with the active engine mounts in the first mode. Accordingly, the vehicle controller may query a lookup table in order to determine whether the active engine mounts are functioning as desired. As discussed above, such a lookup table may comprise lookup table  600  depicted at  FIG. 6 . The vehicle controller may process data corresponding to degraded combustion events, and data recorded via the fuel level indicator (e.g.  187 ), in order to determine whether degraded combustion events are correlated with data recorded from the fuel level indicator. 
     In example timeline  700 , data recorded from the fuel level indicator, corresponding to individual degraded combustion events, is above the threshold vibration level in each of the first predetermined time duration, the second predetermined time duration, and the third predetermined time duration. Thus, it may be understood that in the first predetermined time duration, and the third predetermined time duration, degraded combustion events are not effectively dampened via the active engine mounts configured in the first mode. Instead, the recorded vibrations in the first predetermined time duration, second predetermined time duration, and third predetermined time duration, are all indicated to be correlated with degraded combustion events. As such, the results of the active engine mount test diagnostic are consistent with outcome C, described above with regard to  FIG. 6 . More specifically, it may be determined that the active engine mounts are stuck in the second mode (e.g. stiffening mode). While example timeline depicts a condition where the active engine mounts are stuck in the second mode, other example outcomes, such as outcome A or B, discussed above with regard to  FIG. 6 , may be indicated under conditions where the active engine mounts are indicated to be functioning as desired (e.g. outcome A), or responsive to an indication that active engine mounts are stuck in the first mode (e.g. outcome B). 
     Accordingly, at time t 5 , it is indicated that the active engine mounts are not functioning as desired, indicated by plot  740 . Responsive to the indication that the active engine mounts are not functioning as desired, a flag may be set at the controller, and a malfunction indicator light (MIL) may be illuminated to notify the vehicle operator (where present) of the need to service the vehicle. Furthermore, as the first through third predetermined time periods corresponding to the active engine mount test diagnostic procedure are indicated to be complete, conditions are no longer indicated to be met for conducting the active engine mount test diagnostic, illustrated by plot  715 . With conditions no longer being met for conducting the active engine mount test diagnostic, fueling to the preselected cylinder is enabled to resume. For example, the controller may command the fuel injector configured to provide fuel to the preselected cylinder to resume injection of fuel. Still further, engine RPM may be returned to default RPM prior to commencement of the test diagnostic. While not explicitly illustrated, it may be understood that in a case where an A/C compressor was cycled during the test diagnostic, the A/C compressor may be returned to default conditions prior to the test. Similarly, while not explicitly illustrated, spark provided to the engine cylinders that do not comprise the preselected cylinder for which fuel injection was stopped, may be resumed operation in a default operational state. For example, spark may be commanded to a non-advanced state. Between time t 5  and t 6 , the vehicle resumes traveling, indicated by plot  710 . 
     In this way, an active engine mount test diagnostic procedure may be conducted on a vehicle during an idle stop. In some examples, the test may be conducted on an autonomously driven vehicle such that a diagnosis may be made as to whether the active engine mounts are functioning as desired, even under circumstances where a vehicle operator or other passengers may not be present. However, such an example is not meant to be limiting, and the active engine mount test diagnostic may additionally or alternatively be conducted on vehicles not configured for autonomous driving, such as regular gasoline (or other fuel blend) vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, etc. 
     The technical effect is to recognize that for vehicles with actively controllable engine mounts, under static conditions such as engine idle conditions, engine vibrations may readily be induced by shutting off fueling to a preselected engine cylinder. With the engine vibrations induced via shutting off fueling to the preselected cylinder, vehicle chassis vibrations may be monitored under conditions where the induced vibrations are expected to be dampened, and under conditions where the induced vibrations are not expected to be dampened. By monitoring for whether the induced vibrations are dampened, or not, while controlling the active engine mounts to both dampening modes and stiffening modes, it may be determined as to whether the active engine mounts are functioning as desired, are stuck in the dampening mode, or are stuck in the stiffening mode. By periodically determining whether the active engine mounts are functioning as desired, vehicle system complications arising from active engine mounts that are not functioning as desired may be reduced. 
     In one example, a method may include indicating degradation of an active engine mount by inducing degraded combustion events in a preselected engine cylinder, and operating the active engine mount in multiple modes, the indication responsive to chassis vibration during each of the modes. 
     The systems described herein, and with reference to  FIGS. 1-4 , along with the methods described herein and with reference to  FIG. 5 , may enable one or more systems and one or more methods. In one example, a method comprises indicating degradation of an active engine mount by inducing degraded combustion events in a preselected engine cylinder, and operating the active engine mount in multiple modes, the indication responsive to an amount of vehicle chassis vibration during each of the modes. In a first example of the method, the method further includes wherein the amount of the vehicle chassis vibration is based on a level of fuel slosh in a fuel tank that provides fuel to the engine, where the level of fuel slosh is indicated via a fuel level sensor. A second example of the method optionally includes the first example, and further includes wherein operating the active engine mount in multiple modes further comprises: commanding the active engine mount to a first, dampening mode of active engine mount operation for a first predetermined duration, followed by commanding the active engine mount to a second, stiffening mode of active engine mount operation for a second predetermined duration, and then commanding the active engine mount again to the first, dampening mode of active engine mount operation for a third predetermined duration; and wherein default operation of the active engine mount includes commanding the active engine mount to the first, dampening mode at idle conditions to absorb undesired chassis vibration, and commanding the active engine mount to the second, stiffening mode at higher engine speeds and loads to reduce undesired engine motion. A third example of the method optionally includes any one or more or each of the first and second examples, and further includes wherein indicating degradation of the active engine mount further comprises: determining whether vibrations stemming from the vehicle chassis correlate with the degraded combustion events during controlling the active engine mounts to the first mode and the second mode; indicating the active engine mount is functioning as desired responsive to vehicle chassis vibrations not correlating with degraded combustion events in the first mode, but where vehicle chassis vibrations are correlated with the degraded combustion events in the second mode; indicating the active engine mounts are stuck in the first mode responsive to vehicle chassis vibrations not correlating with the degraded combustion events in the first mode, and where vehicle chassis vibrations are not correlated with the degraded combustion events in the second mode; and indicating the active engine mounts are stuck in the second mode responsive to vehicle chassis vibrations correlating with the degraded combustion events in the first mode, and where vehicle chassis vibrations are also correlated with the degraded combustion events in the second mode. A fourth example of the method optionally includes any one or more or each of the first through third examples, and further includes wherein determining whether vibrations stemming from the vehicle chassis correlate with degraded combustion events during controlling the active engine mounts to the first mode and the second mode further comprises: indicating that the vibrations stemming from the vehicle chassis correlate with the degraded combustion events responsive to the vibrations stemming from the vehicle chassis being above a threshold vibration level within a threshold time of the degraded combustion events. A fifth example of the method optionally includes any one or more or each of the first through fourth examples, and further includes wherein inducing degraded combustion events in the preselected cylinder further comprises: shutting off fueling to the preselected engine cylinder by commanding a fuel injector configured to provide fuel to the preselected engine cylinder to stop injection of fuel to the preselected engine cylinder. A sixth example of the method optionally includes any one or more or each of the first through fifth examples, and further comprises increasing vehicle chassis vibration by one or more of advancing spark in one or more remaining cylinders, the remaining cylinders comprising cylinders that do not comprise the preselected engine cylinder, via one or more spark plug(s) configured to provide spark to the one or more remaining cylinders; increasing and decreasing a speed of an engine of the vehicle in a cyclical fashion; turning on a compressor for an air conditioning system for a duration, and turning off the compressor for another duration, in a cyclical fashion; and/or commanding an air intake throttle configured to enable air to be inducted into the engine, to a predetermined angle. A seventh example of the method optionally includes any one or more or each of the first through sixth examples, and further comprises commanding or maintaining application of one or more wheel brakes for one or more wheels of the vehicle, commanding or maintaining engaged an electronic parking brake for one or more wheels of the vehicle, and maintaining a vehicle transmission configurable to at least a park mode, a drive mode, and a reverse mode, in a drive mode of operation. 
     An example of a system for a vehicle comprises an engine with one or more engine cylinders; one or more active engine mounts configured to isolate engine vibrations from a vehicle chassis and a vehicle cabin, and controllable to a first, dampening mode, and a second, stiffening mode; a fuel tank configured to supply fuel to the engine; a fuel level indicator positioned in the fuel tank; and a controller storing instructions in non-transitory memory, that when executed, cause the controller to: responsive to an indication that preconditions for an active engine mount test diagnostic procedure are met: actively induce degraded combustion events in a preselected engine cylinder; command the one or more active engine mounts to the dampening mode for a first predetermined time duration, then command the one or more active engine mounts to the stiffening mode for a second predetermined time duration, then command the one or more active engine mounts to the dampening mode for a third predetermined time duration while degraded combustion events are occurring in the preselected engine cylinder; monitor vehicle vibrations via the fuel level indicator during the first predetermined time duration, during the second predetermined time duration, and during the third predetermined time duration; and indicate that the one or more active engine mounts are functioning as desired responsive to vehicle vibrations as monitored via the fuel level sensor being dampened below a vibration threshold during the first predetermined time duration and the third predetermined time duration, but not during the second predetermined time duration. In a first example of the system, the system further includes wherein the controller further stores instructions in non-transitory memory, that when executed, cause the controller to: indicate that the one or more active engine mounts are stuck in the first, dampening mode, responsive to vehicle vibrations as monitored via the fuel level indicator being dampened below the vibration threshold during each of the first, second, and third predetermined time durations; and indicate that the one or more active engine mounts are stuck in the second, stiffening mode, responsive to vehicle vibrations as monitored via the fuel level indicator being above the vibration threshold during each of the first, second, and third predetermined time durations. A second example of the system optionally includes the first example, and further comprises one or more fuel injectors configured to deliver fuel to the one or more engine cylinders; and wherein the controller further stores instructions in non-transitory memory, that when executed, cause the controller to: command a fuel injector configured to deliver fuel to a preselected engine cylinder to stop injection of fuel, in order to actively induce degraded combustion events in the preselected engine cylinder. A third example of the system optionally includes any one or more or each of the first and second examples, and further comprises one or more spark plugs configured to provide spark to the one or more engine cylinders; and wherein the controller further stores instructions in non-transitory memory, that when executed, cause the controller to: advance spark in one or more remaining cylinders, where the remaining cylinders include engine cylinders that do not comprise the preselected engine cylinder, during the active engine mount test diagnostic procedure. A fourth example of the system optionally includes any one or more or each of the first through third examples, and further includes wherein preconditions for the active engine mount test diagnostic procedure being met include one or more of an engine idle conditions, a duration of time elapsing since a prior active engine mount test diagnostic procedure, a fuel level in the fuel take between ten percent and ninety percent of a capacity of the fuel tank, an indication of a remote engine start event; and/or an indication that the vehicle is not occupied. A fifth example of the system optionally includes any one or more or each of the first through fourth examples and further includes wherein the indication that the vehicle is not occupied is based on one or more of seat load cells, door sensing technology, and/or onboard cameras. A sixth example of the system optionally includes any one or more or each of the first through fifth examples and further comprises an antilock brake system for increasing or decreasing hydraulic pressure to one or more vehicle wheel brakes; an electronic parking brake; a transmission coupled between the engine and one or more of the vehicle wheels; and wherein the controller further stores instructions in non-transitory memory, that when executed, cause the controller to: in response to the indication that preconditions for the active engine mount test diagnostic procedure are met: command or maintain application of the wheel brakes; command or maintain application of the electronic parking brake; and command the transmission to a drive mode of operation. A seventh example of the system optionally includes any one or more or each of the first through sixth examples and further comprises an air conditioning system coupled to the engine, including a compressor; and wherein the controller further stores instructions in non-transitory memory, that when executed, cause the controller to: in response to the indication that preconditions for the active engine mount test diagnostic procedure are met, command the compressor on for a duration, and then off for another duration, during the active engine mount test diagnostic procedure, in a cyclical fashion. An eighth example of the system optionally includes any one or more or each of the first through seventh examples, and further includes wherein the controller further stores instructions in non-transitory memory, that when executed, cause the controller to: in response to the indication that preconditions for the active engine mount test diagnostic procedure are met, increase and decrease engine speed in a cyclical fashion during the active engine mount test diagnostic procedure. 
     Another example of a method comprises during propelling an automomous vehicle at least in part via an engine, isolating engine vibration from a cabin and a chassis of the vehicle via one or more active engine mounts controllable to at least a dampening mode and a stiffening mode, and in response to predetermined conditions for an active engine mount test diagnostic procedure being met: actively inducing a plurality of degraded combustion events to increase vehicle vibration; controlling the active engine mounts to the dampening mode, followed by the stiffening mode, and then returning the active engine mounts to the dampening mode while the degraded combustion events are occurring; indicating whether the active engine mounts are functioning as desired, are stuck in the dampening mode, or are stuck in the stiffening mode, based on a plurality of fuel slosh events in a fuel tank configured to provide fuel to the engine, as monitored via a fuel level indicator; and wherein predetermined conditions for the active engine mount test diagnostic procedure being met include on or more of an engine idle condition, a duration of time elapsing since a prior active engine mount test diagnostic, a fuel level in the fuel tank between ten percent and ninety percent of a capacity of the fuel tank, an indication of a remote engine start event; and/or an indication that the vehicle is not occupied. In a first example of the method, the method further comprises indicating that the active engine mounts are functioning as desired responsive to the plurality of fuel slosh events as monitored via the fuel level indicator being dampened below a threshold during each of the dampening modes, but where the plurality of fuel slosh events are above the vibration threshold during the stiffening mode; indicating that the active engine mounts are stuck in the dampening mode responsive to the plurality of fuel slosh events as monitored via the fuel level indicator being dampened below the threshold during each of the dampening modes, and the stiffening mode; and indicating that the active engine mounts are stuck in the stiffening mode responsive to the plurality of fuel slosh events as monitored via the fuel level indicator being above the threshold during each of the dampening modes, and the stiffening mode. A second example of the method optionally includes the first example, and further includes wherein actively inducing the plurality of degraded combustion events further comprises: stopping fuel injection to a preselected engine cylinder; and wherein vehicle vibration is further increased by one or more of commanding a transmission coupled to one or more wheels of the vehicle to a drive mode of operation; commanding an electronic parking brake coupled to one or more of the wheels to an engaged configuration; repeatedly cycling an air conditioning system compressor coupled to the engine on and off during the active engine mount test diagnostic procedure; commanding a throttle configured to enable air induction to the engine to a predetermined angle; advancing spark provided to remaining engine cylinders, the remaining engine cylinders comprising engine cylinders that are not the preselected engine cylinder; and/or repeatedly increasing and decreasing a speed of the engine in a cyclical fashion during the active engine mount test diagnostic procedure. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.