Abstract:
A mechanism for determining whether a malfunctioning pressure sensor has returned to a normal or acceptable operating range. The mechanism includes controllers and methods that perform a “good check” on the sensor to determine whether the sensor has returned to normal or acceptable operation after a malfunction has been detected. When a previously-malfunctioning sensor passes the “good check,” warning lights (or tell-tale) indicators are shut off and systems that relied upon information from the malfunctioning sensor return to normal operation.

Description:
RELATED APPLICATION 
     The present application claims the benefit of prior filed U.S. Provisional Patent Application No. 61/236,407 filed on Aug. 24, 2009, the entire content of which is hereby incorporated by reference. 
     This application is related to the following U.S. Patent Applications: U.S. patent application Ser. No. 12/860,362, filed on Aug. 20, 2010 entitled GOOD CHECKING FOR VEHICLE WHEEL SPEED SENSORS; and U.S. patent application Ser. No. 12/860,370, filed on Aug. 20, 2010 and entitled GOOD CHECKING FOR VEHICLE LONGITUDINAL ACCELERATION SENSOR; and U.S. patent application Ser. No. 12/860,376, filed on Aug. 20, 2010 and entitled GOOD CHECKING FOR VEHICLE LATERAL ACCELERATION SENSOR; and U.S. patent application Ser. No. 12/860,389, filed on Aug. 20, 2010 and entitled GOOD CHECKING FOR VEHICLE BRAKE LIGHT SWITCH; and U.S. patent application Ser. No. 12/860,407, filed on Aug. 20, 2010 and entitled GOOD CHECKING FOR VEHICLE STEERING ANGLE SENSOR; and U.S. patent application Ser. No. 12/860,418, filed on Aug. 20, 2010 and entitled GOOD CHECKING FOR VEHICLE YAW RATE SENSOR. 
    
    
     BACKGROUND 
     Modern vehicles include computer systems for controlling engine emissions, vehicle braking, and a variety of other items. The systems require data in order to function, such as oxygen level data for controlling engine emissions and wheel speed data for controlling braking. This data is generally supplied by sensors located throughout the vehicle. To ensure the integrity of the data provided by the sensors, controllers perform malfunction testing on the sensors (or the signals or data the sensors provide). If a sensor malfunction is detected (in other words, there is an error in the sensor output or sensor data), a warning light or similar indicator can be activated. 
     SUMMARY 
     While current vehicle systems are designed to monitor the functioning or operation of vehicle sensors and determine when a sensor malfunction occurs, such systems lack, at least in general, robust abilities for determining when the sensor malfunction ends. For example, a sensor malfunction might be caused by a powerful source of electromagnetic interference (“EMI”). Such a circumstance might occur if a vehicle passes near an electrical power generation plant, a radar or broadcast installation, or similar location. Once the vehicle moves outside the range of the EMI, the output from the sensor might return to within an acceptable range. However, in many vehicles, once a sensor malfunction occurs, the only way in which the malfunction or error may be cleared is to have a mechanic or technician access the system, check its operation, and perform an act that resets the system or otherwise removes the error. 
     A check of the sensor signal based on a re-detection by the failure monitoring function can be used as a mechanism to determine if a sensor has returned to normal operation. However, “good checking” is more than this. In general, malfunction monitoring functions are designed to avoid misdetection. On the other hand, “good check” functions are, in general, designed to avoid a false good check, i.e., a good check function has smaller tolerances for deviations and fewer conditions on the driving situation to perform the evaluation. Or, in other words, the tolerances and conditions used in good checking are different than those used to detect a malfunction. 
     Embodiments of the invention provide a mechanism for automatically determining whether a malfunctioning sensor has returned to a normal or acceptable operating range. In the parlance of the inventors, embodiments of the invention perform a “good check” on the sensor to determine whether the sensor has returned to normal or acceptable operation after a malfunction has been detected. When a previously-malfunctioning sensor passes the “good check,” warning lights (or tell-tale) indicators are shut off and systems that relied upon information from the malfunctioning sensor return to normal operation. 
     In one embodiment, the invention provides a controller for determining whether a previously-detected, vehicle-sensor malfunction still exists. The controller includes an electronic, non-volatile memory and an electronic processing unit connected to the electronic, non-volatile memory. The electronic processing module includes a malfunction monitoring module, a failure handling module, and a signal checking module. 
     The malfunction monitoring module monitors the operation of a pressure sensor and generates a fault signal when the pressure sensor malfunctions. The fault signal contains fault information and causes a tell-tale indicator to be activated or a vehicle control system (such as an engine control system, traction control system, vehicle stability system or the like) to modify its operation from a first operating state to a second operating state. The failure handling module stores the fault information and corresponding drive cycle information in the electronic, non-volatile memory. 
     The signal checking module retrieves the drive cycle information from the electronic, non-volatile memory and performs a good check or signal check on information from the pressure sensor. The signal check verifies that a pressure sensor offset compensation function is active for a predetermined time and that a pressure sensor offset is less than a predetermined threshold. Alternatively, the signal check verifies that a test pulse on the pressure sensor completes successfully without generating a pressure sensor test pulse fault. If the pressure sensor passes the signal or good check, the signal checking module generates a reset signal that causes the tell-tale indicator to be deactivated, the vehicle control system to resume operation in the first operating state, or both. 
     In some embodiments, the signal checking module performs the first signal check on information from the pressure sensor by verifying that at least one pressure sensor offset compensation function is active for a predetermined active time and verifying that an offset value for the pressure sensor is less than a predetermined threshold. The signal checking module verifies that the at least one pressure sensor offset compensation function is active for the predetermined active time by verifying that a pressure sensor positive offset compensation function and a pressure sensor negative offset compensation function are active for the predetermined active time. The signal checking module performs the first signal check on the information from the pressure sensor by verifying that an absolute value of a difference between an actual value of the pressure sensor and the offset value for the pressure sensor is less than a predetermined failure amount. The signal checking module performs the first signal check on information from the pressure sensor while a vehicle monitored by the pressure sensor is traveling substantially forward on a substantially straight path. The signal checking module generates a reset signal if the pressure sensor passes the first signal check, the reset signal configured to cause at least one of the first tell-tale indicator to be deactivated and the first vehicle control system to resume operation in the first operating state. 
     In some embodiments, the malfunction monitoring module is configured to monitor the operation of a brake light switch and generate a second fault signal if the brake light switch malfunctions, the second fault signal containing second fault information and configured to cause at least one of a second tell-tale indicator to be activated and a second vehicle control system to modify its operation from a first operating state to a second operating state. 
     In some embodiments, the failure handling module causes second drive cycle information and second fault information to be stored in the electronic, non-volatile memory. 
     In some embodiments, the signal checking module retrieves the second drive cycle information and the second fault information from the electronic, non-volatile memory, performs a second signal check on information from the brake light switch, and if the pressure sensor passes the first signal check and the brake light switch passes the second signal check, generating a reset signal, the reset signal configured to cause at least one of the second tell-tale indicator to be deactivated and the second vehicle control system to resume operation in the first operating state. The signal checking module performs the second signal check on the information from the brake light switch by verifying that the brake light switch exhibits a predetermined pattern. The predetermined pattern includes a low signal for a predetermined time, then a high signal for a predetermined time, and then a second low signal for a predetermined time. The signal checking module performs the first signal check on the information from the pressure sensor by verifying that a pressure sensor test pulse completes successfully without generating a pressure sensor test pulse fault. The signal checking module performs the first signal check on the information from the pressure sensor while a vehicle monitored by the pressure sensor is traveling substantially forward on a substantially straight path or the vehicle monitored by the pressure sensor is substantially stationary. 
     In another embodiment, the invention provides a controller for determining whether a previously-detected, vehicle-sensor malfunction still exists. The controller includes an electronic, non-volatile memory and an electronic processing unit connected to the electronic, non-volatile memory. The electronic processing module includes a malfunction monitoring module, a failure handling module, and a signal checking module. The malfunction monitoring module monitors the operation of a pressure sensor and a brake light switch and generates a fault signal when the pressure sensor and the brake light switch malfunction. The fault signal contains fault information and causes a tell-tale indicator to be activated or a vehicle control system to modify its operation from a first operating state to a second operating state. The failure handling module stores the fault information and corresponding counter or cycle information (referred to as “drive cycle” information) in the electronic, non-volatile memory. 
     The signal checking module retrieves the drive cycle information from the electronic, non-volatile memory and performs a signal check on both the pressure sensor and the brake light switch. The signal check executed on the pressure sensor verifies that a pressure sensor offset compensation function is active for a predetermined time and that a pressure sensor offset is less than a predetermined threshold. The signal check executed on the brake light switch verifies that the brake light switch exhibits a predetermined pattern. If the pressure sensor and the brake light switch each pass their signal checks, the signal checking module generates a reset signal that causes the tell-tale indicator to be deactivated, causes the vehicle control system to resume operation in the first operating state, or both. 
     Other embodiments of the invention provide a method, executed by a controller including an electronic processing unit and an electronic, non-volatile memory, for determining whether a previously-detected, vehicle-sensor malfunction still exists. The method includes monitoring (with a malfunction monitoring module executed by the electronic processing unit) the operation of at least one of a pressure sensor and a brake light switch and generating a fault signal (containing fault information) when at least one of the pressure sensor and the brake light switch malfunctions. The method also includes activating a tell-tale indictor or modifying the operation of a vehicle control system from a first operating state to a second operating state when the fault signal is generated. In addition, the method includes storing the fault information and corresponding drive cycle information in the electronic, non-volatile memory using a failure handling module executed by the electronic processing unit. 
     The method also includes retrieving the drive cycle information and performing a signal check on information from at least one of the pressure sensor and the brake light switch. Performing a signal check on the pressure sensor includes verifying that a pressure sensor offset compensation function is active for a predetermined time and that a pressure sensor offset is less than a predetermined threshold or verifying that a pressure sensor pulse test completes successfully without generating a pressure sensor test pulse fault. Performing a signal check on the brake light switch includes verifying that the brake light switch exhibits a predetermined pattern. If at least one of the pressure sensor and the brake light switch pass their signal checks, a reset signal is generated by the signal checking module. The reset signal causes the tell-tale indicator to turn off, the vehicle control system to resume operation in the first operating state, or both. 
     In some embodiments, performing the signal check includes verifying that at least one pressure sensor offset compensation function is active for a predetermined active time and verifying that an offset value for the pressure sensor is less than a predetermined threshold. Verifying that at least one pressure sensor offset compensation function is active for the predetermined active time includes verifying that a pressure sensor positive offset compensation function and a pressure sensor negative offset compensation function are active for the predetermined active time. Performing the signal check includes verifying that an absolute value of a difference between an actual value of the pressure sensor and the offset value for the pressure sensor is less than a predetermined failure amount. Performing the signal check includes verifying that a pressure sensor test pulse completes successfully without generating a pressure sensor test pulse fault. Performing the signal check includes verifying that the brake light switch exhibits a predetermined pattern. Verifying that the brake light switch exhibits a predetermined pattern includes verifying that the brake light switch generates a low signal for a predetermined time, then a high signal for a predetermined time, and then a second low signal for a predetermined time. Performing the signal check includes performing the signal check while a vehicle monitored by the pressure sensor and the brake light switch is traveling substantially forward on a substantially straight path or is substantially stationary. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vehicle including a vehicle control system according to one embodiment of the invention. 
         FIG. 2  schematically illustrates the vehicle control system of  FIG. 1  according to one embodiment of the invention. 
         FIG. 3  schematically illustrates the functional operation of modules of the vehicle control system of  FIG. 2  according to one embodiment of the invention. 
         FIG. 4  illustrates a first pressure sensor signal check performed by the signal checking module of  FIG. 3  according to one embodiment of the invention. 
         FIG. 5  illustrates a second pressure sensor signal check performed by the signal checking module of  FIG. 3  according to another embodiment of the invention. 
         FIGS. 6   a - c  illustrate a first brake light switch test of  FIG. 5  according to one embodiment of the invention. 
         FIG. 7  illustrates a third pressure sensor signal check performed by the signal checking module of  FIG. 3  according to one embodiment of the invention. 
         FIG. 8   a  illustrates the values of a cycle flag, a monitoring flag, a detection flag, and a completion flag during the third pressure sensor signal check with a successful outcome (i.e., passed good check). 
         FIG. 8   b  illustrates the values of a cycle flag, a monitoring flag, a detection flag, and a completion flag during the third pressure sensor signal check with an unsuccessful outcome (i.e., failed good check). 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     It should also be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components, may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific configurations illustrated in the drawings are intended to exemplify embodiments of the invention. Alternative configurations are possible. 
       FIG. 1  illustrates a vehicle  10  including a vehicle control system  11 . The vehicle control system  11  includes a brake pedal  14 . A pressure sensor (“PS”)  14   a  is associated with a master cylinder of a hydraulic brake system and senses the amount of pressure in the brake system. The amount of pressure in the brake system is dependent upon actuation of the brake pedal  14 , in the sense that “lightly tapping” the brake pedal  14  causes relatively little pressure to be applied to the brakes, whereas “stomping” on the pedal cause a relatively large amount of pressure to be applied to the brakes. Information output by the pressure sensor  14   a  is transmitted over a connection or network, such as a controller area network (“CAN”) bus  15 . Other components connected to the bus  15  may receive the information from the pressure sensor  14  and use that information to control other aspects of the vehicle  10 . For example, a controller  16  receives information from the pressure sensor  14   a  over the bus  15 . In some embodiments, the controller  16  provides electronic stability control (“ESC”) functionality. For example, when the controller  16  detects a loss of steering control (e.g., understeer or oversteer), the controller  16  automatically applies one or more individual brakes  17  to help steer the vehicle  10  in a desired direction. In some embodiments, the controller  16  also reduces engine power when it detects a skid or slide of the vehicle  10  until the vehicle operator regains control of the vehicle  10 . 
     As shown in  FIG. 1 , the vehicle control system  11  also includes a brake light switch (“BLS”)  18 . The BLS  18  is wired to one or more brake lights  19  (wiring not shown). When an operator presses down the brake pedal  14 , the pedal  14  presses down and creates contact with the BLS  18 , which completes a circuit between the brake lights  19  and a power source, such as the vehicle&#39;s battery (not shown). With the circuit completed, the brake lights  19  are illuminated. 
     The BLS  18  is also connected to the bus  15  and sends information to other components also connected to the bus  15 , such as the controller  16 . The BLS  18  sends information over the bus  15  indicating whether the circuit between the BLS  18  and the brake lights  19  is complete (i.e., whether the brake lights are illuminated). For example, if the circuit is complete and the brake lights are being illuminated, the BLS  18  outputs a power or “high” signal to the bus  15 . Alternatively, if the circuit is incomplete and the brake lights  19  are not being illuminated, the BLS  18  outputs a no-power or “low” signal to the bus  15 . 
     As shown in  FIG. 1 , the control system  11  includes the controller  16 , the bus  15 , and a plurality of sensors. The sensors can include one or more wheel speed sensors  21 , a yaw rate sensor  22 , a steering sensor  23 , a pitch sensor  24 , a roll sensor  25 , a longitudinal acceleration sensor  26 , a lateral acceleration sensor  27 , the brake light switch  18 , and the brake pressure sensor  14   a.    
       FIG. 2  schematically illustrates the vehicle control system  11  of  FIG. 1  in greater detail. The numerous sensors depicted in  FIG. 1  are represented generally by boxes  20  (Sensor 1 . . . Sensor N). As also shown in  FIG. 2 , the controller  16  includes an input/output interface  32 , an electronic processing unit (“EPU”)  34 , and one or more memory modules, such as a random access memory (“RAM”) module  36   a  and an electronically erasable programmable read-only memory (“EEPROM”) module  36   b . As shown in  FIG. 2 , the input/output interface  32  transmits and/or receives information over the bus  15 . In other embodiments, the input/output interface  32  transmits and/or receives information directly to and/or from the sensors  20  rather than over the bus  15 . 
     The EPU  34  receives the information from the input/output interface  32  and processes the information by executing one or more applications or modules. The applications or modules are stored in memory (such as EEPROM  36   b ). The EPU  34  also stores information (e.g., information received from the bus  15  or information generated as a result of executing instructions) in memory. For example, as described below, the EPU  34  stores drive cycle information and fault information in the EEPROM  36   b.    
       FIG. 3  illustrates the functional operation of applications or modules executed by the EPU  34  of the controller  16 . As shown in  FIG. 3 , the EPU  34  executes a malfunction monitoring module  40 , a failure handling module  42 , a vehicle control system  44  (such as an electronic stability control (“ESC”) program or application), and a signal checking module  46 . The malfunction monitoring module  40  receives sensor signals from the sensors  20  over the bus  15  (e.g., through the input/output interface  32 ) and saves the sensor signals to memory. As shown in  FIG. 3 , the malfunction monitoring module  40  saves filtered and/or compensated sensor signals to memory rather than raw data. For example, over time a sensor  20  may become dirty or damaged, which can affect the sensor&#39;s operation. The malfunction monitoring module  22  applies an offset (positive or negative) to the signals received from a particular sensor  20  to compensate for the sensor&#39;s deterioration and stores the compensated sensor signal to memory. As described below, if a particular sensor&#39;s offset gets too large (in either the positive or the negative direction), the malfunction monitoring module  40  determines that the sensor  20  is malfunctioning or faulty and generates a fault signal. The malfunction monitoring module  22  also saves additional information to memory, such as sensor offsets, detected faults, and other statistical information about a particular sensor (e.g., an average sensor reading, a median sensor reading, etc.). 
     The main function or purpose of the malfunction monitoring module  40  is to determine if a particular sensor is malfunctioning or faulty. For example, as mentioned above, if a sensor&#39;s offset becomes too large, the malfunction monitoring module  40  may determine that the sensor  20  is malfunctioning. A variety of other algorithms and techniques for determining whether a sensor is malfunction can also be used including those disclosed in, for example, U.S. Pat. No. 6,834,221. As shown in  FIG. 3 , when the malfunction monitoring module  40  detects a malfunctioning or faulty sensor, the module  40  generates a fault signal and sends the fault signal to the fault handling module  42 . The fault signal includes fault information based on the particular fault or malfunction observed by the malfunction monitoring module  40 . The failure handling module  42  stores the fault information and corresponding counter information, (which is referred to as “drive cycle information”) in memory. The drive cycle information indicates what tests should be performed by the signal checking module  46  during the next drive cycle (e.g., the next time during which malfunction testing is performed) to determine whether a previously-detected fault still exists. For example, if the malfunction monitoring module  40  detects that the pressure sensor  14   a  is malfunctioning and generates a fault signal, the fault handling module  42  saves drive cycle information to memory indicating that the signal checking module  46  should check the pressure sensor  14   a  during a subsequent cycle to determine whether the previously-detected pressure sensor fault still exists. 
     As shown in  FIG. 3 , the vehicle control system  44  requests the currently-detected faults from the failure handling module  42 . The failure handling module  42  retrieves the stored fault information from memory and sends the fault information to the vehicle control system  44 . In other embodiments, the vehicle control system  44  obtains currently-detected faults from the malfunction monitoring module  40 , the RAM  36   a , the bus  15 , or other components included in the system  11 . 
     After obtaining them, the vehicle control system  44  determines how to handle the current faults. In some embodiments, the vehicle control system  44  activates one or more warning lights or tell-tales in the vehicle  10  (e.g., on the vehicle&#39;s dashboard or instrument panel) in response to the currently-detected faults. In some applications, the warning lights or tell-tales provide information to the vehicle operator regarding the one or more faulty sensors  20 . In other applications, the warning lights or tell-tales provide information about a vehicle system. For example, if a faulty brake pressure sensor is detected, the vehicle may activate a warning light regarding the anti-lock braking system rather than activating a specific warning light regarding the brake pressure sensor. Thus, the warning light or tell tale may only provide general information to the driver regarding the existence of a fault, whereas the control system  44  knows the specific nature of the fault. 
     Although not strictly required, in almost all instances the vehicle control system  44  modifies its operation in response to faults determined by the malfunction monitoring module  40  in addition to activating a warning light or tell tale. For example, if a particular sensor  20  is malfunctioning, the vehicle control system  44  changes its operation from a first operating state (e.g., ON) to a second operating state (e.g., OFF). In the first or “normal” operating state, the vehicle control system  44  operates as intended or programmed using all the data it receives from the sensors  20 . In the second operating state, the vehicle control system turns itself off (as noted) or, alternatively, operates in a state where information from faulty sensors is ignored, but control is still provided based on information from the remaining, non-malfunctioning sensors. Yet another option is for the vehicle control system  44  to operate in a manner in which some of its functionality or features are reduced. The factors determining the exact parameters of the second state of operation of the vehicle control system is a measure of the criticality or importance of the information provided by the malfunctioning sensor. For example, information from a yaw rate sensor may be critical to certain vehicle control functions (such as ESC), but may be unimportant or less critical to others (such as traction control). Thus, if a yaw rate sensor malfunction is detected, traction control may continue to function based on information from other sensors, but ESC might be turned off. If the vehicle control system  44  deactivates or modifies its functionality or other types of vehicle control or monitoring functionality, the vehicle control system  44  can activate one or more warning lights or tell-tales that warn the vehicle operator of the modified operating state. 
     The signal checking module  46  retrieves drive cycle information stored in the EEPROM  36   b  and performs various good checks or signal checks to determine whether a previously-detected sensor malfunction still exists. In some embodiments, the signal checking module  46  is initialized during each new ignition cycle and retrieves the stored drive cycle information upon each initialization. In other embodiments, the signal checking module  46  retrieves stored drive cycle information from memory at various times while the controller  16  is operating. 
     Performing a signal check includes testing current readings or information from a particular sensor  20 . Therefore, the signal checking module  46  obtains current sensor readings from memory, the bus  15 , the malfunction monitoring module  40 , or from other components of the system  11 . The current sensor readings include compensated or filtered sensor signals or information, raw sensor information, current sensor offsets, and/or other statistical information about a particular sensor  20 . Once the signal checking module  46  obtains current sensor readings, the module  46  compares the information to one or more thresholds to determine whether a previously-detected fault still exists. The signal checking module  46  can also execute a test on a sensor by sending information to a sensor and observing the response. 
     If the signal checking module  46  determines that a previously-detected fault doesn&#39;t exist anymore, the module  46  resets the corresponding fault information and/or drive cycle information in memory. The signal checking module  46  resets the drive cycle information by generating a reset signal. The failure handling module  42  receives the reset signal and updates the fault information and/or drive cycle information stored in memory to indicate that the previously-detected fault no longer exists (e.g., by deleting the previous fault and/or drive cycle information or setting a fault bit or flag to an “okay” or “no fault” value). When the vehicle control system  44  subsequently requests the current faults from the failure handling module  42 , the failure handling module  42  informs the vehicle control system  44  that the previously-detected fault no longer exists (e.g., by failing to list the fault as one of the current faults). The vehicle control system  44  re-assesses the current faults and, in some embodiments, deactivates a previously-activated warning light or tell-tale within the vehicle  10  and/or returns its operation back to a first or original operating state (e.g., an ON state). 
     On the other hand, if the signal checking module  46  determines that the previously-detected fault still exists, the signal checking module  46  sets the corresponding fault and/or drive cycle information in memory. By setting the corresponding fault and/or drive cycle information in memory, the signal checking module  46  ensures that the stored fault information and/or drive cycle information continues to indicate that the fault exists so that (1) the vehicle control system  44  is informed of the existence of the fault and (2) the signal checking module  46  will run another signal check on the fault during subsequent operation. The signal checking module  46  sets the fault and/or drive cycle information by generating a set signal. The failure handling module  42  receives the set signal and ensures that the fault information and/or drive cycle information in memory continues to indicate that the fault still exists. In other embodiments, the signal checking module  46  simply fails to reset the fault and/or drive cycle information (e.g., fails to generate and output a reset signal), which retains the fault and/or drive cycle information in the same state as before the signal checking module  46  performed its signal checks. 
       FIG. 4  illustrates a first pressure sensor signal check  50  performed by the signal checking module  46  after the malfunction monitoring module  40  detects, for example, a pressure sensor offset malfunction. As described above, a pressure sensor offset malfunction occurs when an offset for the pressure sensor (“pressure sensor offset”) becomes greater than a predetermined threshold. In some embodiments, when the malfunction monitoring module  40  detects a pressure sensor offset malfunction, an anti-lock braking system (“ABS”) warning light and an ESC failure tell-tale are illuminated. 
     As shown in  FIG. 4 , the first step of the first pressure sensor signal check includes determining whether the retrieved drive cycle information includes drive cycle information for a pressure sensor offset malfunction (step  52 ). The retrieved drive cycle information can include a flag or bit (e.g., a pressure sensor offset drive cycle bit or flag) that is set if a pressure sensor offset malfunction is detected by the malfunction monitoring module  40 . If this flag is not set, the signal checking module  46  ends the signal check  50 . 
     If this flag is set, the signal checking module  46  executes a first pressure sensor test  54  (e.g., a pressure sensor offset test). Generally, the first pressure sensor test  54  determines whether one or more pressure sensor offset compensation functions have been active for a predetermined time and whether a current pressure sensor offset is less than a predetermined threshold. For example, as shown in  FIG. 4 , step  56  includes determining whether one or more pressure sensor offset compensation functions are active. In some embodiments, this step includes determining whether a positive pressure sensor offset compensation function and a negative pressure sensor offset compensation function are active. The malfunction monitoring module  40  enables these pressure sensor offset compensation functions after certain operations of the vehicle  10 , such as after the vehicle is driven with a predetermined minimum acceleration. The signal checking module  46  uses information obtained from memory and/or the malfunction monitoring module  40  to determine whether the required offset compensation functions are active. 
     As part of the initial step  56 , the signal checking module  46  also verifies that the absolute value of the difference between a current sensor reading from the pressure sensor  14   a  and a current pressure sensor offset is less than a predetermined failure amount (e.g., 0 to 100 bar, which varies based on the characteristics of the vehicle). By performing this check, the signal checking module  46  verifies that the pressure sensor offset has not grown as large as or larger than the actual pressure sensor readings. For example, if the pressure sensor&#39;s current sensor reading is 4 bar and the current pressure sensor offset is 7 bar (causing the compensated sensor signal output by the malfunction monitoring module  40  to be approximately 11 bar), the pressure sensor  14   a  is probably still malfunctioning because its offset is greatly changing its current sensor readings. This large offset probably indicates that the pressure sensor  14   a  is still malfunctioning and, therefore, needs to be serviced or replaced. 
     As shown in  FIG. 4 , if the signal checking module  46  determines that the proper pressure sensor offset compensation functions are not active or determines that a current pressure sensor reading and a current pressure sensor offset differ by at least the predetermined failure amount, the signal checking module  46  ends the first pressure sensor signal check  50 . Before ending the first pressure sensor signal check  50 , the module  46  decrements a pressure sensor offset active counter at step  58 . As described below in more detail, the pressure sensor offset active counter tracks how long a pressure sensor offset compensation function has been active. The signal checking module  46  also sets a pressure sensor offset signal check flag at step  50  before ending the signal check  50 . In some embodiments, the signal checking module  46  sets the pressure sensor offset signal check flag by generating a set signal. The failure handling module  42  receives the set signal and ensures that the stored fault information and/or drive cycle information continue to indicate that the pressure sensor offset malfunction exists. 
     Alternatively, if the signal checking module  46  determines that the proper pressure sensor offset compensation functions are active and the current pressure sensor reading and the current pressure sensor offset differ by less than the predetermined failure amount (step  56 ), the signal module  46  determines whether the proper pressure sensor offset compensation functions have been active for at least a predetermined active time (e.g., 0 to 120 seconds, which varies depending on the characteristics of the vehicle). As described above, the signal checking module  46  uses a pressure sensor offset active counter to track how long a compensation function has been active. The active counter is initialized to 0 seconds when a pressure sensor offset compensation function is activated and the signal checking module  46  or another component in the system  11  increments and decrements the counter accordingly. 
     If the pressure sensor offset active counter is set to less than the predetermined active time (step  62 ), the checking module  46  increments the counter (step  64 ). Next, the signal checking module  46  determines if the counter is set to at least the predetermined active time (step  66 ). If so, the signal checking module  46  also checks if the current pressure sensor offset is less than or equal to a predetermined threshold (e.g., 0 to 100 bar, which varies based on the characteristics of the vehicle) (step  66 ). If both conditions of step  66  are satisfied, the signal checking module  46  concludes that the previously-detected pressure sensor offset malfunction no longer exists. In other words, if the malfunction monitoring module  40  has been actively calculating an offset for the pressure sensor  14   a  for at least the predetermined active time and the current pressure sensor offset is less than the predetermined threshold, the signal checking module  46  concludes that a pressure sensor offset malfunction no longer exists. 
     As shown in  FIG. 4 , if the signal checking module  46  determines that the pressure sensor offset malfunction no longer exists, the signal checking module  46  resets a pressure sensor offset signal check flag to indicate that the previously-detected malfunction no longer exists (step  68 ). In some embodiments, the signal checking module generates a reset signal to complete this step. The failure handling module  42  receives the reset signal and ensures that the fault information and/or drive cycle information stored in memory no longer indicate that a pressure sensor offset malfunction exists. When the vehicle control system  44  subsequently requests the current faults from the failure handling module  42  (as described above with respect to  FIG. 3 ), the vehicle control system  44  will be informed that the pressure sensor offset malfunction no longer exists. Based on this updated information, the vehicle control system  44  responds. It deactivates a warning light or a tell-tale and/or modifies its operation back to a first or original operating state (e.g., an active and fully functional state), or both. After resetting the pressure sensor offset signal check flag at step  68 , the signal checking module  36  ends the first pressure sensor signal check  50 . 
     On the other hand, as shown in  FIG. 4 , if the signal checking module  46  determines that the pressure sensor offset malfunction still exists (i.e., fails step  66 ), the signal checking module  46  sets the pressure sensor offset signal check flag at step  70 , as described above for step  60 , and ends the first pressure sensor signal check  50 . 
       FIG. 5  illustrates a second pressure sensor signal check  80  performed by the signal checking module  46 . The signal checking module  46  executes the signal check  80  after the malfunction monitoring module  40  detects, for example, a pressure sensor offset malfunction, as described above with respect to  FIG. 4 , and a BLS permanent high malfunction. A BLS permanent high malfunction occurs when the malfunction monitoring module  40  determines that the BLS  18  has been outputting a “high” signal for a predetermined time. In some embodiments, when the malfunction monitoring module  40  detects a pressure sensor offset malfunction and a BLS permanent high malfunction, an ABS warning light and an ESC failure tell-tale are illuminated. 
     As shown in  FIG. 5 , the first step of the second pressure sensor signal check  80  includes determining whether the retrieved drive cycle information specifies that a pressure sensor offset malfunction and BLS permanent high malfunction have occurred (step  81 ). The retrieved drive information can includes a flag or bit (e.g., a BLS plausibility failure drive cycle bit or flag) that is set accordingly. If this flag is not set, the signal checking module  46  ends the signal check  80 . If this flag is not set, the signal checking module  46  ends the signal check  80 . If this flag is set, the signal checking module  46  executes (1) a first BLS test  82  (e.g., a BLS permanent high test) and (2) the first pressure sensor test  54 , as described above with respect to  FIG. 4  (step  84 ). 
       FIGS. 6   a - c  illustrate the first BLS test  82 , which determines whether the BLS  18  exhibits a predetermined pattern. The pattern includes a low signal, followed by a high signal, and followed by second low signal. It is to be understood that the second low signal may be substantially the same as the first signal or may vary therefrom. This particular pattern indicates that the BLS  18  is not stuck in a permanent high state. In some embodiments, the BLS  18  must exhibit each signal of the pattern for a predetermined time (e.g., 0 to 1 second, which varies based on the characteristics of the vehicle). The predetermined time may be the same for each signal of the pattern or may be different. 
     The signal checking module  46  uses a BLS “OK” Counter to detect the predetermined pattern. The BLS “OK” Counter includes a bit for each state of the predetermined pattern, and the signal checking module  46  sets each bit as it observes each state. Therefore, the BLS “OK” Counter includes 3 bits, wherein the bits represent whether the BLS  18  has demonstrated the first (low signal), second (high signal), and third (low signal) state of the desired pattern. Initially the BLS “OK” Counter bits is set to 000 (i.e., the decimal value of zero) to indicate that the BLS  18  has not yet demonstrated any of the states of the pattern. As the signal checking module  46  observes each state, the module  46  sets the corresponding bit. In particular, after the module  46  observes the first state of the pattern, the signal checking module  46  sets the first bit of the BLS “OK” Counter (i.e., bit  0 ) to “1,” which sets the BLS “OK” Counter to a decimal value of 1. Similarly, after the module  46  observes the second state of the pattern, the module  46  sets the second bit of the BLS “OK” Counter (i.e., bit  1 ) to “1,” which sets the BLS “OK” Counter to a decimal value of 3. Finally, after the module  46  observes the final state of the pattern, the module  46  set the third bit of the BLS “OK” Counter (i.e., bit  2 ) to “1,” which sets the BLS “OK” Counter to a decimal value of 7. 
       FIG. 6   a  illustrates the portion of the first BLS test  82  that determines whether the BLS  18  is demonstrating the first state of the desired pattern (i.e., a low signal). The signal checking module  46  starts by determining if the BLS “OK” Counter is set to the decimal value of 0 (step  90   a ). If the BLS “OK” Counter is not set to 0, the signal checking module  46  has already observed at least one of the states of the desired pattern, and the signal checking module  46  proceeds to check for other states of the pattern (see  FIGS. 6   b  and  6   c ). 
     If the BLS “OK” Counter does equal 0 (step  90   a ), the signal checking module  46  determines whether the BLS  18  is currently demonstrating a low signal (step  92   a ). If the BLS  18  is not currently outputting a low signal, the signal checking module resets a filter timer (step  94   a ) (whose function is described below) and ultimately exits the test  82 . The test  82  may be subsequently re-initiated (e.g., in subsequent initiations of the signal checking module  46 ) to check for the first pattern state. 
     If, however, the BLS  18  is currently outputting a low signal (step  92   a ), the signal checking module  46  determines whether the BLS  18  has been outputting this signal for the predetermined time (step  96   a ). The signal checking module  46  uses a filter timer to track how long the BLS  18  outputs a particular signal. The filter timer is initially set to 0 when the test  82  is started and is reset after a particular pattern state is observed (see step  99   a ) or when a particular state is not initially observed (see step  94   a ). As shown in  FIG. 6   a , if the BLS  18  has not been outputting a low signal for at least the predetermined time, the signal checking module  46  increments the filter timer (step  97   a ) and ultimately exits the test  82 . 
     However, if the BLS  18  has been outputting a low signal for at least the predetermined time (step  96   a ), the BLS  18  has satisfied the first state of the desired pattern and the signal checking module  46  sets a first bit (i.e., bit  0 ) of the BLS “OK” Counter to “1” (i.e., setting the BLS OK Counter to the decimal value of 1) (step  98   a ). In addition, the signal checking module  46  resets the filter timer (step  99   a ) and proceeds to check for the second state of the desired pattern (see  FIG. 6   b ). 
       FIG. 6   b  illustrates the portion of the test  82  that determines whether the BLS  18  is outputting a high signal for at least the predetermined time and  FIG. 6   c  illustrates the portion of the test  82  that determines whether the BLS  18  is outputting a low signal for at least the predetermined time. Because these portions of the test  82  are similar to the portion illustrated in  FIG. 6   a , the details are not described in detail. 
     Returning to  FIG. 5 , at step  84 , after executing the first BLS test  82 , the signal checking module  46  executes the pressure sensor offset test  42 , as described above with respect to  FIG. 4 . If both tests  82 ,  42  are passed, the signal checking module  46  resets the BLS plausibility signal check flag to indicate that the previously-detected malfunctions of the BLS  18  and pressure sensor  14   a  no longer exist (step  100 ). To reset the BLS plausibility signal check flag, the signal checking module generates a reset signal. The failure handling module  42  receives the reset signal and ensures that the fault information and drive cycle information stored in memory no longer indicate that a BLS plausibility malfunction exists. When the vehicle control system  44  subsequently requests the current faults from the failure handling module  42 , the vehicle control system  44  is informed that the BLS plausibility malfunction no longer exists. Based on this information, the vehicle control system  44  deactivates a warning light or tell-tale and/or modifies its operation back to a first operating state (e.g., an ON and fully functional state). After resetting the BLS plausibility signal check flag, the signal checking module  46  exits the signal check  80 . 
     If tests  82  and  42  are not passed, the signal checking module  46  exits the signal check  80 . By not resetting the BLS plausibility signal check flag before exiting the signal check  80 , the signal checking module  46  retains the fault and/or drive cycle information stored in memory in the same state as before the signal checking module  46  executed the signal check  80 . Alternatively, the signal checking module  46  may set the BLS plausibility signal check flag before exiting the second pressure sensor signal check  80  by generating a set signal. The failure handling module  42  receives the set signal and ensures that the fault information or drive cycle information stored in memory continues to indicate that the BLS versus pressure sensor plausibility malfunction exists. 
       FIG. 7  shows a third pressure sensor signal check  110  performed by the signal checking module  46 . The signal check  110  includes a second pressure sensor test  112  (e.g., a pressure sensor test pulse test) and is executed after the malfunction monitoring module  40  detects a pressure sensor sensitivity malfunction. In some embodiments, when the malfunction monitoring module  40  detects a pressure sensor malfunction, an ABS warning light and an ESC failure tell-tale are illuminated. 
     As shown in  FIG. 7 , the signal checking module  46  initially obtains the stored fault and/or drive cycle information and determines whether the retrieved drive cycle information includes drive cycle information for a pressure sensor sensitivity or test pulse failure (step  114 ). If so, the signal checking module  46  executes the second pressure sensor test  112  at step  116 . Otherwise, the signal checking module  46  exits the third pressure sensor signal check  110 . 
     As shown in  FIG. 7 , the second pressure sensor test  112  determines whether a test pulse sent to the pressure sensor  14   a  was completed and whether any test pulse faults were detected (step  116 ). The pressure sensor  14   a  is associated with multiple flags or bits, such as a drive cycle flag, a monitoring flag, a failure detection flag, and a completion flag, which are affected by a test pulse. The signal checking module  46  evaluates these flags after the test pulse to perform the test  112 .  FIG. 8   a  illustrates the status of these flags after a successful pressure sensor test pulse, and  FIG. 8   b  illustrates the status of these flags after an unsuccessful pressure sensor test pulse. Using the status of the flags, the signal checking module  46  determines whether the completion flag is set and whether the failure detection flag is set (step  116 ). If so, the pressure sensor  14   a  passes the second pressure sensor test  112  and the signal checking module  46  resets the pressure sensor test pulse signal check flag to indicate that a pressure sensor sensitivity malfunction no longer exists (step  118 ). However, if the completion flag is not set or the completion flag is set but the failure detection flag is also set, the pressure sensor  14   a  fails the second pressure sensor test  112  and the signal checking module  46  exits the third pressure sensor signal check  110 . 
     In some embodiments, the signal checking module  46  executes particular signal checks during certain driving maneuvers. For example, the signal checking module  46  may execute the signal checks  50  and  100  when the vehicle  10  is traveling in a forward direction on a substantially straight path. The module  46  may execute the signal check  80  when the vehicle  10  is substantially stationary or when it is traveling in a forward direction on a substantially straight path. The signal checking module  46  may also execute other tests during a particular signal check or may only perform individual tests included in a particular signal check. For example, the signal checking module  46  may execute the first BLS test  82  as part of a signal check without also performing the first pressure sensor test  42 , such as when the BLS  18  malfunctions but the pressure sensor  14   a  does not. 
     Thus, the invention provides, among other things, a controller for determining whether a previously-detected, vehicle sensor malfunction still exists by executing various signal checks using sensor-related information. Various features and advantages of the invention are set forth in the following claims.