Emission control diagnostic system and method

A method of diagnosing an emission control system of an internal combustion engine, comprising during degraded performance of the emission control system, dynamically identifying a relationship between a plurality of operating conditions of the emission control system; and correlating the relationship to a plurality of potential sources of degraded performance of the emission control system to identify at least one degraded source among the plurality of potential sources.

TECHNICAL FIELD

The present application relates to the field of automotive emission control systems and methods.

BACKGROUND AND SUMMARY

Selective catalytic reduction (SCR) systems have been used to reduce automotive emissions. However, degraded performance in SCR systems may be related to a plurality of sources. For example, the injection system, the SCR catalyst, and the reductant quality as well as various other potential sources may be root cause for degraded performance.

One way to identify a potential source of degraded performance may be to determine degraded performance of the emission control system whereby an inspection of the system may be performed for diagnosis. However, under some conditions, such as during travel in remote areas, a mechanical diagnose of the system may be inconvenient. Further, it may be desirable to isolate a source of potential degraded performance within the emission control system so as to operate the vehicle such that various other strategies may still be used to control emissions.

In one approach, a method may be used that identifies which of a plurality of potential degradation sources is at least partially responsible for causing degraded output of a urea-based NOx reduction system by considering and correlating each of the plurality of sources. In another approach, a method of operating an internal combustion engine having an emission control system is provided. The method comprises, during degraded performance of the emission control system, dynamically identifying a relationship between a plurality of operating conditions of the emission control system, and correlating the relationship to one or more sources of degraded performance of the emission control system. Additionally, or alternatively, the method may distinguish one or more sources of degraded performance from a plurality of potential sources of said degraded performance based on said relationship. In this way, accurate identification of a source of degradation among a plurality of potential sources is possible, even when each of the potential sources may be responsible for the degradation.

In still another approach, a method of diagnosing an emission control system may be used that comprises: during degraded performance of the emission control system, dynamically identifying a relationship between a plurality of operating conditions of the emission control system, and correlating the relationship to a plurality of potential sources of degraded performance of the emission control system to identify at least one degraded source among said plurality of potential sources.

DETAILED DESCRIPTION OF THE DEPICTED EMBODIMENTS

Referring now toFIG. 1, direct injection internal combustion engine10, comprising a plurality of combustion chambers and controlled by electronic engine controller12, is shown. Combustion chamber30of engine10includes combustion chamber walls32with piston36positioned therein and connected to crankshaft40. In one example, piston36includes a recess or bowl (not shown) to form selected levels of stratification or homogenization of charges of air and fuel. Alternatively, a flat piston may also be used.

Combustion chamber30is shown communicating with intake manifold44and exhaust manifold48via intake valve52, and exhaust valve54. Fuel injector66is shown directly coupled to combustion chamber30for delivering liquid fuel directly therein in proportion to the pulse width of signal fpw received from controller12via conventional electronic driver68. Fuel is delivered to fuel system (not shown) including a fuel tank, fuel pumps, and a fuel rail. In some embodiments, engine10may include a plurality of combustion chambers each having a plurality of intake and/or exhaust valves.

Intake valve52may be controlled by controller12via electric valve actuator (EVA)51. Similarly, exhaust valve54may be controlled by controller12via EVA53. During some conditions, controller12may vary the signals provided to actuators51and53to control the opening and closing of the respective intake and exhaust valves. The position of intake valve52and exhaust valve54may be determined by valve position sensors55and57, respectively. In alternative embodiments, one or more of the intake and exhaust valves may be actuated by one or more cams, and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems to vary valve operation. For example, combustion chamber30may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT.

Intake manifold42may include a throttle62having a throttle plate64. In this particular example, the position of throttle plate64may be varied by controller12via a signal provided to an electric motor or actuator included with throttle62, a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle62may be operated to vary the intake air provided to combustion chamber30among other engine cylinders. The position of throttle plate64may be provided to controller12by throttle position signal TP. Intake manifold42may include a mass air flow sensor120and a manifold air pressure sensor122for providing respective signals MAF and MAP to controller12.

Controller12activates fuel injector66so that a desired air-fuel ratio mixture is formed. Controller12controls the amount of fuel delivered by fuel injector66so that the air-fuel ratio mixture in chamber30can be selected to be substantially at (or near) stoichiometry, a value rich of stoichiometry, or a value lean of stoichiometry. Further, controller12is configured to activate fuel injector66so that multiple fuel injections may be performed during a cycle.

Exhaust manifold gas sensor126is shown coupled to exhaust passage48upstream of catalytic converter70. Sensor126may be any suitable sensor for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor.

Catalytic converter70is shown in communication with exhaust manifold48. In some embodiments, Catalytic converter70may be a diesel oxidation catalyst. An emission control diagnostic system74is shown in communication with catalytic converter70. Controller12is configured to control emission control system. This feature is described in more detail below.

Controller12is shown inFIG. 1as a conventional microcomputer including: microprocessor unit102, input/output ports104, an electronic storage medium of executing programs and calibration values, shown as read-only memory chip106in this particular example, random access memory108, keep alive memory110, and a conventional data bus.

Controller12is shown receiving various signals from sensors coupled to engine10, in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor112coupled to cooling sleeve114; a profile ignition pickup signal (PIP) from Hall effect sensor118coupled to crankshaft40giving an indication of engine speed (RPM); throttle position TP from throttle position sensor120; and absolute Manifold Pressure Signal MAP from sensor122. Engine speed signal RPM is generated by controller12from signal PIP in a conventional manner and manifold pressure signal MAP provides an indication of engine load.

Combustion in engine10can be of various types, depending on operating conditions. WhileFIG. 1depicts a compression ignition engine, it will be appreciated that the embodiments described below may be used in any suitable engine, including but not limited to, diesel and gasoline compression ignition engines, spark ignition engines, direct or port injection engines, etc. Further, various fuels and/or fuel mixtures such as gasoline, diesel, H2, ethanol, methane, and/or combinations thereof may be used

FIG. 2shows an illustration of an example of emissions control diagnostic system74of engine10in more detail. Generally, the components described herein may operate to monitor performance of the system and to further identify potential sources of degraded performance as needed. The emissions control diagnostic system is shown coupled to an exhaust system202at a location upstream of a catalytic converter70(shown inFIG. 1), such as a diesel oxidation catalyst. Further, the emission control diagnostic system may generally include a SCR catalyst204, an injection system206, and a diagnostic system208. In addition, the emission control diagnostic system may include a diesel particulate filter (not shown).

SCR catalyst204may facilitate the reduction of NOx in the exhaust from engine10by a reagent. In some embodiments, the reductant may be liquid urea. In particular, NOx from the exhaust system reacting with urea in the SCR catalyst may form more environmentally benign products such as nitrogen, carbon dioxide, and water for emission into the atmosphere. Some exemplary SCR reactions are as follows.

First, urea added to exhaust system202may decompose into ammonia as follows:
CO(NH2)2→NH3+HNCO
HNCO+H2O→NH3+CO2

Ammonia may, in turn, react with NOx in the SCR catalyst according to various different reaction pathways, including but not limited to one or more of the following:
4NO+4NH3+O2→4N2+6H2O
2NO2+4NH3+O2→3N2+6H2O
6NO2+8NH3+→7N2+12H2O
NO+NO2+2NH3→2N2+3H2O

It may be desirable to introduce an amount of urea to the exhaust system generally derived from the above NOx reduction reaction stoichiometries or a look-up table stored in controller12. In particular, the amount of urea introduced to exhaust system202may be based on information from one or more sensors. For example, the output signal from a sensor, such as exhaust gas manifold sensor126shown inFIG. 1, may indicate an amount of NOx in the exhaust. As such, controller12may prompt injection system206to introduce an amount of urea to the exhaust system accordingly where the amount of urea injected may be expected to substantially consume the urea and convert a substantial portion of the NOx. Further, a minimum conversion efficiency may be selected to define acceptable performance of the emission control system such that NOx may be substantially removed from the exhaust. For example, a predetermined minimum conversion efficiency may be used as a threshold where conversion of NOx below the predetermined conversion efficiency may indicate degraded performance of the emission control system.

Injection system206may store and/or supply a reductant to the SCR catalyst. In some embodiments, the injection system may include a reductant storage device210containing liquid urea. Further, the injection system may include ancillary components to supply the urea to exhaust system, such as supply pump214, reductant valve212, and nozzle216, for example. Under some conditions, the reductant valve may be configured to facilitate an amount of urea from the reductant storage device to be transported by the supply pump through the nozzle into the exhaust system coupled to the SCR catalyst. For example, controller12may prompt an amount of urea to be injected corresponding to the amount of NOx leaving engine10as detected by sensor126(not shown inFIG. 2) so as to substantially consume the urea and reduce the NOx in the exhaust. However, under other conditions, the amount of urea injected may be adjusted to be different from the amount determined to substantially consume urea and reduce NOx. In particular, the amount of urea may be adjusted to diagnose performance of the emission control system as described in more detail below.

A diagnostic system208may monitor the performance of the emission control system and identify one or more potential sources of degraded performance. In particular, controller12may monitor performance of the emission control system such that degraded performance may be indicated where performance may be determined based on various operating conditions. As such, the diagnostic system may include one or more sensors arranged in communication with controller12to detect various operating conditions of the emission control diagnostic system. In some embodiments, the diagnostic system may include a temperature sensor218, a NOx sensor220, and an ammonia sensor222, although various other sensors, devices, or combinations thereof may also provide feedback to the controller. For example, temperature sensor218may be fluidically disposed upstream the nozzle whereat urea may be introduced to the exhaust system. Further, NOx sensor220and ammonia sensor222may be disposed upstream the SCR catalyst to determine various concentrations in the exhaust of the SCR catalyst. The exemplary sensors described herein may function to determine degraded performance of the emission control system and/or identify potential sources of degraded performance as described in detail below.

Under some conditions, the diagnostic system may indicate acceptable performance in the SCR catalyst. In some embodiments, the ammonia sensor and/or the NOx sensor may be used to determine acceptable performance. For example, ammonia from the decomposition of urea introduced to the exhaust system may substantially reduce the NOx entering the SCR catalyst. Alternately or in addition, urea introduced to the exhaust system may decompose to ammonia whereby ammonia absorbed in the SCR catalyst may be substantially consumed by the NOx entering the SCR catalyst. As such, the NOx sensor and/or the ammonia sensor may indicate substantially low levels of NOx and/or ammonia leaving the SCR catalyst. In this way, the controller may monitor performance of the emission control system based on various operating conditions as sensed by various components as described herein.

However, under some other conditions, the diagnostic system may indicate degraded performance of the SCR catalyst. In some embodiments, a conversion efficiency of the emission control system may be less than a predetermined minimum conversion efficiency. Alternately or in addition, a NOx and/or ammonia concentration may be greater than a predetermined allowable emission level. For example, the amount of ammonia absorbed in the SCR catalyst may not substantially reduce the NOx entering the SCR whereby the NOx sensor may indicate a concentration of NOx greater than a predetermined allowable NOx level leaving the SCR catalyst. In another example, ammonia may not be substantially consumed by NOx in the exhaust stream such that a substantial concentration of ammonia may be detected in the exhaust of the SCR catalyst. In this way, the diagnostic system may indicate degraded performance in the SCR catalyst.

The diagnostic system may be prompted to identify potential sources of the degraded performance described above. In some embodiments, potential sources of degraded performance may include the injector system, the SCR catalyst, a reductant quality, various other sources, or some combination thereof. In particular, various operating conditions, such as temperature, NOx concentration, ammonia concentration, etc. may communicate information associated with potential sources of degraded performance. Further, various operating conditions may be detected concurrently such that a source of degraded performance may be identified. For one example, a substantial NOx concentration leaving the SCR catalyst concurrent with a substantial ammonia concentration at the SCR outlet may indicate the SCR catalyst as a source of degraded performance of the emission control system. As such, the diagnostic system may detect a relationship between operating conditions correlated to a potential problem in the emission control system. In this way, various operating conditions may be concurrently monitored and isolated to identify root cause of degraded performance, with each of the potential sources evaluated. As described in detail below, one approach may monitor various operating conditions of the emission control system and sequentially determine a relationship between the operating conditions to identify one or more sources of degraded performance therein based on concurrently detected operating conditions.

FIG. 3shows a flowchart300of an exemplary method for diagnosing degraded performance in an emission control device. In particular, the method described herein may identify potential sources of degraded performance. Specifically, a relationship between various operating conditions may be sequentially correlated to one or more potential sources of degraded performance of an emission control system as further detailed inFIG. 4andFIG. 5.

Beginning at step310, the diagnostic system detects degraded performance. In particular, the controller may determine degraded performance of the emission control system. As described above, a conversion efficiency, NOx concentration, ammonia concentration, various other conditions, or some combination thereof may be used to determine performance. Under some conditions, the controller may identify degraded performance of the emission control system. As such, an output signal may be sent to the controller indicating degraded performance of the emission control system.

As such, in step320, the controller may be prompted to diagnose degraded performance of the emission control system. In particular, degraded performance of the emission control system may prompt the controller to identify one or more potential sources of degraded performance. Specifically, a relationship between various operating conditions in the emission control system may be correlated to one or more potential sources of degraded performance so as to identify a root cause.

Various conditions in the emission control system may result in degraded performance, as illustrated in detail with respect toFIG. 4. In some embodiments, a source of degraded performance may be the injector system, as detailed below inFIG. 4A. For example, an injector may be clogged such that a reduced amount of urea may be introduced to the exhaust system. In another example, a failure in communication between the controller and the injector system may inhibit or reduce urea injection. In another embodiment, a source of degraded performance may be a damaged or deteriorated SCR catalyst as detailed below inFIG. 4B. In yet another embodiment, a source of degraded performance may be a low reductant quality of the fluid stored in the reductant storage device as detailed inFIG. 4C. For example, a reductant-diluting substance, such as water, may be introduced to the reductant storage device instead of a reductant, such as urea. Further, potential sources of degraded performance, may be associated with various operating conditions wherein the operating conditions may be related to identify root cause.

In some embodiments, the injection system may be prompted to adjust an amount of urea into the exhaust system so as to monitor a response of the emission control system. Consequently, the controller may communicate with one or more sensors to detect various operating conditions in response to an injection adjustment whereby feedback from various sensors may be used to identify one or more potential sources of degraded performance. Further, the controller may sequentially receive feedback from a plurality of sensors whereby a relationship may be determined between various operating conditions based on concurrently detected operating conditions. In this way, the controller may sequentially determine a relationship based on the feedback correlating to one or more sources of degraded performance to identify one or more sources of degraded performance.

In one embodiment, an operating condition may be detected by a sensor such that it may be determined if a potential source may be identified as a source of degraded performance. For example, temperature sensor218may detect a temperature conditions such that the injection system may or may not be identified as a source of degraded performance. Based on feedback from the sensor, the controller may then receive feedback from another sensor such that it may be determined whether another source of degraded performance may be identified as a source of degraded performance. For example, an ammonia sensor222may detect an ammonia concentration at the outlet of the SCR catalyst such that the SCR catalyst may or may not be a potential source of degraded performance. Further, based on feedback detected from a plurality of sensors, such as the temperature and/or the ammonia sensor, the controller may sequentially distinguish the injection system and/or the SCR catalyst as sources of degraded performance from various other potential sources of degraded performance whereby various other potential sources, such as reductant quality, for example, or combinations thereof may or may not further be identified as potential sources of degraded performance. In this way, the emission control diagnostic system may methodically determine root cause of degraded performance as detailed further below inFIG. 5.

In one embodiment, temperature sensor218may be used to determine if the injector system may be a potential source of degraded performance. Under some conditions, a temperature of the exhaust system intermediate to the injection nozzle and the SCR catalyst may at least temporarily drop in response to a urea injection. For example, urea delivered to the exhaust system may result in a temperature drop. However, under other conditions, the temperature sensor may not detect a temperature drop following an adjustment in urea injection. For example, a temperature drop may not be detected when a damaged injector may not deliver a urea injection as prompted. As such, the temperature sensor may be used to monitor a response to a urea injection. In this way, the injection system may be identified as root cause of degraded performance of the emission control system if a reduction in temperature in the exhaust system downstream the nozzle may not be sensed after a change in injection amount.

In another embodiment, if the injection system may not be identified as a source of degraded performance, ammonia sensor222may be used to determine if the SCR catalyst may be a potential source. For example, the injection system may be prompted to adjust an injection amount to the exhaust system whereby the temperature sensor may detect a reduced temperature upstream the SCR catalyst (i.e. the injection system may functional). However, ammonia sensor222may detect high levels of ammonia in the exhaust of the SCR catalyst. For example, the SCR catalyst may be damaged such that ammonia may not be absorbed but instead substantially pass through into the exhaust of the SCR catalyst. Further, ammonia concentrations leaving the SCR catalyst may be at least partially correlated to an adjustment of a reductant amount. In this way, the SCR catalyst may be diagnosed to be a root cause of degraded performance if unacceptable ammonia levels may correlate to adjustments in reductant flow.

In another embodiment, if the injector system and/or the SCR catalyst may not be identified as a source of degraded performance, various other sources may be identified as root cause. For example, under some conditions, a reductant-diluting substance may be introduced to the reductant storage device. As such, the controller may prompt the injection system to deliver the reductant-diluting substance to the exhaust system whereby a temperature sensor may detect a reduced temperature although urea may not be injected to the exhaust. Further, the ammonia sensor may not detect substantial levels of ammonia leaving the SCR catalyst. Consequently, a non-ammonia containing substance may be introduced to the exhaust system so as to facilitate a reduction in temperature at the temperature sensor as well as maintain low levels of ammonia leaving the SCR catalyst. In this way, reductant quality in the reductant storage device may be diagnosed as root cause of degraded performance. As described in the above embodiments, method300may diagnose one or more potential sources of degraded performance by sequentially determining a relationship between the operating conditions as further detailed inFIG. 5.

At step330, one or more potential sources of degraded performance may be indicated. In some embodiments, the controller may prompt an indicator light to illuminate corresponding to the location of the root cause determined by the diagnostic system. In various other embodiments, the controller may enable various other emission control strategies until a root cause of degraded performance may be fixed. In this way, the emission control diagnostic system may determine an appropriate strategy to compensate for degraded performance of the emission control system until root cause may be fixed.

FIG. 4is a schematic illustration of embodiments of potential sources of degraded performance in the emission control system. In particular, the embodiments described below schematically illustrate feedback from various sensors in response to a change in the amount of urea introduced to the exhaust system where the feedback may be correlated to one or more potential sources of degraded performance as described above. Specifically, the embodiments shown inFIG. 4may illustrate a plurality of relationships between various operating conditions where the relationships may be correlated to one or more potential sources of degradation of the emission control system. As such, one or more sensors may be filled solid where a solid indicator may be used to symbolically represent an undesirable operating condition, such as a concentration of NOx, a concentration of ammonia, or a temperature condition, for example. Further, although in the embodiments described herein, NOx sensor220may indicate degraded performance, various conditions alternate to NOx concentration may be used to indicate degraded performance of the emission control system.

Referring specifically to the embodiment ofFIG. 4A, feedback from temperature sensor218may identify the injection system as a potential source of degraded performance. In particular, a substantial NOx concentration at the SCR outlet may trigger an adjustment in reductant injection whereby the temperature sensor downstream the nozzle may detect an undesirable temperature condition. For example, a temperature may not drop as expect following a reductant injection. As such, a relationship between a substantial NOx concentration at the SCR outlet and a temperature condition wherein the temperature may not drop in response to an adjustment in reductant injection may be correlated to a problem in the injection system. As described above, a clogged injector and/or an electronic failure may deter triggering a urea injection whereby the temperature sensor may not detect a temperature drop following a change in urea injection. As such, if a reduction in temperature may not be detected, the injector system may be identified as root cause of degraded performance of the emission control system.

Referring now to the embodiment ofFIG. 4B, feedback from ammonia sensor222may identify the SCR catalyst as a potential source of degraded performance. In particular, a substantial NOx concentration at the SCR outlet may trigger an adjustment in reductant injection whereby a concentration of ammonia at the SCR outlet may be detected. As such, a relationship between a substantial NOx concentration and an ammonia concentration at the SCR outlet in response to an adjustment in reductant injection may be correlated to a problem in the SCR. As described above, a damaged or deteriorated SCR catalyst may result in high levels of ammonia in the exhaust of the SCR catalyst. As such, if a substantial concentration of ammonia may be detected in the exhaust of the SCR catalyst, the SCR catalyst may be identified as root cause of degraded performance of the emission control system.

Referring specifically to the embodiment ofFIG. 4C, degraded reductant quality may be identified as a potential source of degraded performance if neither the injector system nor the SCR catalyst may be identified as root cause for degraded performance of the emission control system. In particular, a substantial NOx concentration at the SCR outlet may trigger an adjustment in reductant injection whereby the temperature sensor downstream the nozzle may detect a temperature drop and a substantial concentration of ammonia may not be detected at the SCR outlet. As such, a relationship between a substantial NOx concentration at the SCR outlet, an expected temperature drop following a reductant injection, and an acceptable level of ammonia at the outlet of the SCR catalyst may be correlated to various other problems, such as a reduced reductant quality, degraded injection, etc. In this way, the emission diagnostic system may determine root cause of degraded performance by sequentially detecting a plurality of operating conditions and identifying a source of degraded performance based on a relationship between the operating conditions.

FIG. 5shows a flowchart500of an exemplary method for identifying a potential source of degraded performance. Generally, the method described in flowchart500may enable urea quality sensing, determine degraded performance of the emission control system, then identify root cause of the degraded performance at steady state conditions based on various operating conditions in response to a change in an injection amount from the reductant storage device as described herein.

Method500begins at step502wherein it may be determined if the engine may be operating within predetermined bounds. In particular, the emission control system may not be diagnosed if various engine operating conditions may not be met. In some embodiments, the engine operating conditions may include an exhaust temperature, an engine speed, a vehicle speed, an EGR level, an exhaust back pressure, a fuel quantity, a torque, a coolant temperature, various other engine operating conditions, or some combination thereof. For example, if the engine exhaust temperature may be below a predetermined temperature threshold, the method as described herein may not continue so as to reduce or prevent diagnosis of degraded performance of the system during conditions when low performance may be expected. Further, method500may be disabled during periods of transient operation, such as during a transmission shift, when using a glow plug, during air conditioning, alternating, braking, power steering, etc. In this way, robustness of the method described herein may be improved.

Continuing to step504, method500may enable urea quality sensing if the engine may be operating within the bounds described in step502. As such, the controller may be prompted to begin a process for determining degrading performance whereby root cause of the degraded performance may be identified based on various operating conditions.

Referring now to step506, the controller may determine degraded performance of the emission control system. In particular, as described above, a conversion efficiency, NOx concentration, ammonia concentration, various other conditions, or some combination thereof may be used to determine performance. If degraded performance may not be determined (i.e. conversion efficiency may be greater than a predetermined conversion efficiency, substantially low levels of NOx and/or ammonia in the exhaust of the SCR catalyst, etc.), then method500may return to step502. However, if degraded performance of the emission control system may be determined in the emission control system, then method500may continue to step508.

Next, at step508, it may be determined if the engine may be operating at steady state. In some embodiments, steady-state may be identified based on various engine operating conditions, such as engine speed, pedal position, SCR temperature, etc. If engine operating conditions may not be at steady-state, method500may return to step502. However, if engine operating conditions may be at steady state then method500may continue to step510.

At step510, a reductant injection may be adjusted. In some embodiments, an amount of reductant injected to the exhaust system may be changed. In various other embodiments, an injection profile may be changed continually. For example, a reductant injection may be changed in an oscillating fashion. Further, a reductant injection may be determined as a function of various operating conditions, such as the predetermined engine bounds as described in step502.

Continuing to step512, it may be determined if a change in temperature may be determined in response to the adjustment described in step510. In some embodiments, a change in temperature may be determined as a function of various operating conditions, such as the predetermined engine bounds as described in step502. Further, under some conditions, such as oscillating reductant injection as described in step510, for example, the change in temperature may be integrated to output a signal such that the signal may exhibit increase reliability. Under some a change in temperature may not be determined. For example, the reductant injector may be clogged. Under various other conditions, a change in temperature may be determined. For example, an increase in an amount of urea injected to the exhaust system may result in a temperature drop as detected by temperature sensor218.

If the temperature sensor may not detect a reduction in temperature upstream the reductant injection nozzle, then method500continues to step514whereat the injection system may be identified as root cause for degraded performance of the emission control system. Next, at step522, method500may send a signal to indicate root cause. In some embodiments, an output signal indicating root cause of the emission control system may be sent to the controller. Consequently, the controller may illuminate an indicator light on the dashboard of the vehicle, for example. In another example, a diagnostic code may be stored such that root cause may be determined at a service bay. In yet another example, the controller may enable various other emission control strategies, as described herein. Further, the controller may limit various engine operating conditions, such as limiting engine operation to a number of cycles, until root cause may be rectified.

Referring back to step512, if the temperature sensor may detect a reduction in temperature, then method500continues to step516. At step516, it may be determined if an ammonia concentration may be greater than a predetermined ammonia concentration at the outlet of the SCR catalyst. Under some conditions, an ammonia concentration may be greater than a predetermined or expected ammonia concentration. For example, the SCR catalyst may be damaged. However, under various other conditions, an ammonia concentration may substantially equivalent to a predetermined or expected ammonia concentration.

If an ammonia concentration at the outlet of the SCR catalyst may be greater than a predetermined ammonia concentration, then method500continues to step518whereat the SCR may be identified as root cause for degraded performance of the emission control system. Next, at step522, method500may send a signal to indicate root cause, as described above.

Referring back to step516, if an ammonia concentration at the outlet of the SCR catalyst may be substantially equivalent to a predetermined or expected ammonia concentration, then method500continues to step520. At step520, root cause may be identified by various conditions. In particular, if it may not be determined that root cause may be the injector system nor the SCR catalyst, than root cause may be various other conditions. Specifically, a change in reductant injection may result in a temperature change as indicated at step512(i.e. root cause may not be the injection system) and may result in an acceptable ammonia concentration at the outlet of the SCR catalyst (i.e. root cause may not be the SCR catalyst). However, the emission control system may exhibit degraded performance as determined by NOx sensor220, for example. In one example, root cause may be degraded urea quality. In another example, root cause may be a degraded injection system.

At step516, it may be determined if an ammonia concentration may be greater than a predetermined ammonia concentration at the outlet of the SCR catalyst. Under some conditions, an ammonia concentration may be greater than a predetermined or expected ammonia concentration. For example, the SCR catalyst may be damaged. However, under various other conditions, an ammonia concentration may substantially similar to a predetermined or expected ammonia concentration.