Part 2
ENGINE OBD II MONITORS
Part 2 of 4
Continued From Part 1 Part 1
Cold Start Emission Reduction System Monitor
The PCM uses the cold start emission reduction system monitor to calculate the actual catalyst warm up temperature during a cold start. The actual catalyst warm up temperature calculation uses measured engine speed, measured air mass and commanded spark timing inputs to the PCM. The PCM then compares the actual temperature to the expected catalyst temperature model. The expected catalyst temperature model calculation uses desired engine speed, desired air mass and desired spark timing inputs to the PCM. The difference between the actual and expected temperatures is reflected in a ratio. This ratio is a measure of how much loss of catalyst heating occurred over the period of time and when compared with a calibrated threshold it helps the PCM to determine if the cold start emission reduction system is working correctly. This ratio correlates to tailpipe emissions, and a malfunction indicator lamp (MIL) illuminates when the calibrated threshold is exceeded. The monitor is disabled if a malfunction is present in any of the sensors or systems used for expected catalyst temperature model calculation.
Cold Start Emission Reduction System Monitor Test Operation
- DTC: P050E cold start engine exhaust temperature out of range
- Monitor execution: once per driving cycle, from start up with the cold start emission reduction monitor active
- Monitor sequence: the monitor collects data during first 15 seconds of the cold start
- Monitoring duration: the monitor completes 300 seconds after initial engine start
Cold Start Emission Reduction System Monitor Entry Conditions
- Engine coolant temperature at the start of the monitor is between 1.67°C (35°F) and 37.78°C (100°F)
- Barometric pressure is above 74.5 kPa (22 in-Hg)
- Catalyst temperature at the start of the monitor is between 1.67°C (35°F) and 51.67°C (125°F)
- Fuel level is above 15%
- Power take-off operation is disabled
Comprehensive Component Monitor (CCM)
The CCM monitors for malfunctions in any powertrain electronic component or circuit that provides input or output signals to the PCM that can affect emissions and is not monitored by another OBD II monitor. Inputs and outputs are, at a minimum, monitored for circuit continuity or correct range of values. Where feasible, inputs are also checked for rationality, outputs are also checked for correct functionality.The CCM covers many components and circuits and tests them in various ways depending on the hardware, function, and type of signal. For example, analog inputs such as throttle position or engine coolant temperature are typically checked for opens, shorts and out-of-range values. This type of monitoring is carried out continuously. Some digital inputs like vehicle speed or crankshaft position rely on rationality checks - checking to see if the input value makes sense at the current engine operating conditions. These types of tests may require monitoring several components and can only be carried out under appropriate test conditions.Outputs such as coil drivers are checked for opens and shorts by monitoring a feedback circuit or smart driver associated with the output. Other outputs, such as relays, require additional feedback circuits to monitor the secondary side of the relay. Some outputs are also monitored for correct function by observing the reaction of the control system to a given change in the output command. An idle air control solenoid can be functionally tested by monitoring the idle RPM relative to the target idle RPM. Some tests can only be carried out under the appropriate test conditions. For example, the transmission shift solenoids can only be tested when the PCM commands a shift.The following is an example of some of the input and output components monitored by the CCM. The components monitor may belong to the engine, ignition, transmissions, air conditioning, or any other PCM supported subsystem.
1. Inputs:
a. Air conditioning (ACP) pressure sensor
b. Camshaft position (CMP) sensor
c. Crankshaft position (CKP) sensor
d. Engine coolant temperature (ECT) sensor or cylinder head temperature (CHT) sensor
e. Engine oil temperature (EOT) sensor
f. Fuel rail pressure (FRP) sensor
g. Fuel rail temperature (FRPT) sensor
h. Fuel tank pressure (FTP) sensor
i. Intake air temperature (IAT) sensor
j. Mass air flow (MAF) sensor
k. Throttle position (TP) sensor
2. Outputs:
a. EVAP canister purge valve
b. EVAP canister vent (CV) solenoid
c. Fuel injector
d. Fuel pump (FP)
e. Idle air control (IAC)
f. Intake manifold runner control (IMRC)
g. Shift solenoid
h. Torque converter clutch (TCC) solenoid
i. Wide open throttle A/C cutout (WAC)
3. CCM is enabled after the engine starts and is running. A DTC is stored in KAM and the MIL is illuminated after 2 driving cycles when a malfunction is detected. Many of the CCM tests are also carried out during an on-demand self-test.
Electric Exhaust Gas Recirculation (EEGR) System Monitor
The EEGR system monitor is an on-board strategy designed to test the integrity and flow characteristics of the EGR system. The monitor is activated during EGR system operation and after certain base engine conditions are satisfied. Inputs from the engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), throttle position (TP), crankshaft position (CKP), mass air flow (MAF), and manifold absolute pressure (MAP) sensors are required to activate the EGR system monitor. Once activated, the EGR system monitor carries out each of the tests described below during the engine modes and conditions indicated. Some of the EGR system monitor tests are also carried out during a key on engine off (KOEO) or key on engine running (KOER) self-test.
The EEGR monitor consists of an electrical and functional test that checks the stepper motor and the EEGR system for correct flow. The PCM controls the EEGR valve by commanding from 0 to 52 discreet increments or steps to get the valve from fully closed to fully open respectively. The stepper motor electrical test is a continuous check of the 4 electric stepper motor coils and circuits to the PCM. A malfunction is indicated if an open circuit, short to voltage, or short to ground has occurred in 1 or more of the stepper motor coils or circuits for a calibrated period of time. If a malfunction has been detected, the EEGR system is disabled, setting DTC P0403. Additional monitoring is suspended for the remainder of the drive cycle, or until the next engine startup.After the vehicle has warmed up and normal EEGR flow rates are being commanded by the PCM, the EEGR flow check is carried out. The flow test is carried out once per drive cycle when a minimum amount of exhaust gas is requested and the remaining entry conditions required to initiate the test are satisfied. If a malfunction is detected, the EEGR system, as well as the EEGR monitor, is disabled until the next engine startup.
An EGR flow malfunction is indicated by either a no flow condition or a low flow condition prior to exceeding 1.5 times the applicable emission standard. The criteria used to determine which flow malfunction threshold applies is based upon whether or not the applicable emission standards are exceeded on the federal test procedure test cycle without EGR delivery.
The EGR flow test is done by observing the behavior of 2 different values of MAP - the analog MAP sensor reading, and inferred MAP, (MAP calculated from the MAF, throttle position, RPM, barometric pressure (BARO) and other sensors). Due to the location of the MAF sensor, the calculation of inferred MAP is not compensated for EGR flow. Therefore, it does not account for the effects of EGR flow whereas measured MAP does respond to the effects of EGR flow. The amount of EGR flow can therefore be calculated by looking at the difference between measured MAP and inferred MAP under the correct engine operating conditions.Some differences always exist between measured MAP and inferred MAP due to hardware variations. These variations are learned during steady engine operating conditions without EGR flow and the estimated EGR flow is compensated for these differences. The result of this compensation is values of measured MAP and inferred MAP that are equal under conditions where no EGR is flowing. Hence, when EGR is flowing the increased pressure in measured MAP over inferred MAP represents the pressure change due to EGR flow. This pressure change is normalized to a value between 0 and 1 representing the ratio of measured EGR flow to the scheduled EGR flow and is referred to as the EGR flow degradation index. A value near 1 indicates the system is functioning correctly whereas a value near 0 reflects EGR severe flow degradation.
The EGR flow degradation index is compared to a calibrated threshold to determine if a low flow malfunction has occurred. If an EGR flow malfunction has occurred, the P0400 DTC flow malfunction is registered.If the inferred ambient temperature is less than -7°C (20°F), greater than 54°C (130°F), or the altitude is greater than 8,000 feet (BARO less than 22.5 in-Hg), the EEGR flow test cannot be reliably done. In these conditions, the EEGR flow test is suspended and a timer starts to accumulate the time in these conditions. When the vehicle leaves these extreme conditions, the timer starts to decrement, and if conditions permit, attempts to complete the EGR flow monitor. If the timer reaches 800 seconds, the EEGR flow test is disabled for the remainder of the current driving cycle and the EGR monitor is set to a ready condition.
NOTE: BARO is inferred at engine startup using the KOEO MAP sensor reading. It is updated during high, part-throttle, engine operation.
A DTC P1408, like the P0400, indicates an EGR flow malfunction (outside the minimum or maximum limits) but is only set during the KOER self-test. The P0400 and P0403 are MIL codes. P1408 is a non-MIL code.
Evaporative Emission (EVAP) Leak Check Monitor
The EVAP leak check monitor is an on-board strategy designed to detect a leak from a hole (opening) equal to or greater than 0.508 mm (0.020 inch) in the enhanced EVAP system. The correct function of the individual components of the enhanced EVAP system, as well as its ability to flow fuel vapor to the engine, is also examined. The EVAP leak check monitor relies on the individual components of the enhanced EVAP system to either allow a natural vacuum to occur in the fuel tank or apply engine vacuum to the fuel tank and then seal the entire enhanced EVAP system from the atmosphere. The fuel tank pressure is then monitored to determine the total vacuum lost (bleed-up) for a calibrated period of time. Inputs from the engine coolant temperature (ECT) sensor or cylinder head temperature (CHT) sensor, intake air temperature (IAT) sensor, mass air flow (MAF) sensor, vehicle speed, fuel level input (FLI) and fuel tank pressure (FTP) sensor are required to enable the EVAP leak check monitor.
During the EVAP leak check monitor repair verification drive cycle, clearing the DTCs and resetting the emission monitors information in the PCM bypasses the minimum soak time required to complete the monitor. The EVAP leak check monitor does not run if the key is turned off after clearing the continuous DTCs and resetting the emission monitors information in the PCM. The EVAP leak check monitor does not run if a MAF sensor malfunction is present. The EVAP leak check monitor does not initiate until the heated oxygen sensor (HO2S) monitor is complete.If the vapor generation is high on some vehicle enhanced EVAP systems, where the monitor does not pass, the result is treated as a no test. Therefore, the test is complete for the day.
Some vehicle applications have an engine off natural vacuum (EONV) check as part of the EVAP leak check monitor.
Engine On EVAP Leak Check Monitor
The engine on EVAP leak check monitor is executed by the individual components of the enhanced EVAP system as follows:
1. The EVAP canister purge valve, also known as the vapor management valve (VMV), is used to control the flow of vacuum from the engine and create a target vacuum on the fuel tank.
2. The canister vent (CV) solenoid is used to seal the EVAP system from the atmosphere. It is closed by the PCM (100% duty cycle) to allow the EVAP canister purge valve to obtain the target vacuum on the fuel tank.
3. The FTP sensor is used by the engine on EVAP leak check monitor to determine if the target vacuum necessary to carry out the leak check on the fuel tank is reached. Some vehicle applications with the engine on EVAP leak check monitor use a remote in-line FTP sensor. Once the target vacuum on the fuel tank is achieved, the change in fuel tank vacuum over a calibrated period of time determines if a leak exists.
4. If the initial target vacuum cannot be reached, DTC P0455 (gross leak detected) is set. The engine on EVAP leak check monitor aborts and does not continue with the leak check portion of the test.
For some vehicle applications, if the initial target vacuum cannot be reached after a refueling event and the purge vapor flow is excessive, DTC P0457 (fuel cap off) is set. If the initial target vacuum cannot be reached and the purge flow is too small, DTC P1443 (no purge flow condition) is set.
a. If the initial target vacuum is exceeded, a system flow malfunction exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. The engine on EVAP leak check monitor aborts and does not continue with the leak check portion of the test.
b. If the vacuum increase is quicker than expected, a blocked fuel vapor tube is suspected and if confirmed after an intrusive test, DTC P144A is set.
c. If the target vacuum is obtained on the fuel tank, the change in the fuel tank vacuum (bleed-up) is calculated for a calibrated period of time. The calculated change in fuel tank vacuum is compared to a calibrated threshold for a leak from a hole (opening) of 1.016 mm (0.040 inch) in the enhanced EVAP system. If the calculated bleed-up is less than the calibrated threshold, the enhanced EVAP system passes. If the calibrated bleed-up exceeds the calibrated threshold, the test aborts. The test can be repeated up to 3 times.
d. If the bleed-up threshold is still being exceeded after 3 tests, a vapor generation test must be carried out before DTC P0442 (small leak detected) is set. This is accomplished by returning the enhanced EVAP system to atmospheric pressure by closing the EVAP canister purge valve and opening the CV solenoid. Once the FTP sensor observes the fuel tank is at atmospheric pressure, the CV solenoid closes and seals the enhanced EVAP system.
e. The fuel tank pressure build-up, over a calibrated period of time is compared to a calibrated threshold for pressure build-up due to vapor generation.
f. If the fuel tank pressure build-up exceeds the threshold, the leak test results are invalid due to vapor generation. The engine on EVAP leak check monitor attempts to repeat the test again.
g. If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 is set.
5. If the 1.016 mm (0.40 inch) test passes, the test time is extended to allow the 0.508 mm (0.020 inch) test to run.
a. The calculated change in fuel vacuum over the extended time is compared to a calibrated threshold for a leak from a 0.508 mm (0.020 inch) hole (opening).
b. If the calculated bleed-up exceeds the calibrated threshold, the vapor generation test is run. If the vapor generation test passes (no vapor generation), an internal flag is set in the PCM to run a 0.508 mm (0.020 inch) test at idle (vehicle stopped).
c. On the next start following a long engine off period, the enhanced EVAP system is sealed and evacuated for the first 10 minutes of operation.
d. If the appropriate conditions are met, a 0.508 mm (0.020 inch) leak check is conducted at idle.
e. If the test at idle fails, a DTC P0456 is set. There is no vapor generation test with the idle test.
6. The MIL is activated for DTCs P0442, P0455, P0456, P0457, P1443, and P1450 (or P0446) after 2 occurrences of the same concern and for DTC P144A after a sufficient number of completions. The MIL can also be activated for any enhanced EVAP system component DTCs in the same manner. The enhanced EVAP system component DTCs P0443, P0452, P0453, and P1451 are tested as part of the CCM.
Engine Off Natural Vacuum (EONV) EVAP Leak Check Monitor
The EONV EVAP leak check monitor is executed during key off, after the engine on EVAP leak check monitor is completed. The EONV EVAP leak check monitor determines a leak is present when the naturally occurring change in fuel tank pressure or vacuum does not exceed a calibrated limit during a calibrated amount of time. A separate, low power consuming, microprocessor in the PCM manages the EONV leak check. The engine off EVAP leak check monitor is executed by the individual components of the enhanced EVAP system as follows:
1. The EVAP canister purge valve, also known as the vapor management valve (VMV), is normally closed at key off.
2. The normally open canister vent (CV) remains open for a calibrated amount of time to allow the fuel tank pressure to stabilize with the atmosphere. During this time period the FTP sensor is monitored for an increase in pressure. If pressure remains below a calibrated limit the CV is closed by the PCM (100% duty cycle) and seals the EVAP system from the atmosphere.
3. The FTP sensor is used by the EONV EVAP leak check monitor to determine if the target pressure or vacuum necessary to complete the EONV EVAP leak check monitor on the fuel tank is reached. Some vehicle applications with the EONV EVAP leak check monitor use a remote in-line FTP sensor. If the target pressure or vacuum on the fuel tank is achieved within the calibrated amount of time, the test is complete.
4. The EONV EVAP leak check monitor uses the naturally occurring change in fuel tank pressure as a means to detect a leak in the EVAP system. At key off, a target pressure and vacuum is determined by the PCM. These target values are based on the fuel level and the ambient temperature at key off. As the fuel tank temperature increases, the pressure in the tank increases and as the temperature decreases a vacuum develops. If a leak is present in the EVAP system the fuel tank pressure or vacuum does not exceed the target value during the testing time period. The EONV EVAP leak check monitor begins at key off.
After key off the normally open canister vent (CV) remains open for a calibrated amount of time to allow the fuel tank pressure to stabilize with the atmosphere. During this time period the FTP sensor is monitored for an increase in pressure. If pressure remains below a calibrated limit the CV is closed by the PCM (100% duty cycle) and seals the EVAP system from the atmosphere.
If the pressure on the fuel tank decreases after the EVAP system is sealed, the EONV EVAP leak check monitor begins to monitor the fuel tank pressure. When the target vacuum is exceeded within the calibrated amount of time the test completes and the fuel tank pressure and time since key off information is stored. If the target vacuum is not reached in the calibrated amount of time, a leak is suspected and the fuel tank pressure and time since key off information is stored.
If the pressure on the fuel tank increases after the EVAP system is sealed, but does not exceed the target pressure within a calibrated amount of time the CV is opened to allow the fuel tank pressure to again stabilize with the atmosphere. After a calibrated amount of time the CV is closed by the PCM and seals the EVAP system. When the fuel tank pressure exceeds either the target pressure or vacuum within the calibrated amount of time the test completes and the fuel tank pressure and time since key off information is stored. If the target pressure or vacuum is not reached in the calibrated amount of time, a leak is suspected and the fuel tank pressure and time since key off information is stored.
When a leak is suspected, the PCM uses the stored fuel tank pressure and time since key off information from an average run of 4 tests to suspect a leak. Some vehicles use an alternative method of a single run of 5 tests to determine the presence of a leak. If a leak is still suspected after 2 consecutive runs of 4 tests, (8 total tests) or 1 run of 5 tests, DTC P0456 is set and the MIL is illuminated.
5. The EONV EVAP leak check monitor is controlled by a separate low power consuming microprocessor inside the PCM. The fuel level indicator, fuel tank pressure, and battery voltage are inputs to the microprocessor. The microprocessor outputs are the CV solenoid and the stored test information. If the separate microprocessor is unable to control the CV solenoid or communicate with other processors DTC P260F is set.
6. The MIL is activated for DTCs P0456 and P260F. The MIL can also be activated for any enhanced EVAP system component DTCs in the same manner. The enhanced EVAP system component DTCs P0443, P0446, P0452, P0453, and P1451 are tested as part of the CCM.
Continued in Part 3 Part 3