Hell Mr Pitbull2008. The gas engine on your vehicle has multiple emission system that it monitors constantly to verify that it will meet government requirments for tail pipe and evaporative emissions. When a particular test fails it will set a code in the computer to give a technician a diagnostic path to follow to find the cause, and subsequently turn on the lamp so that you know there is a fault. The following is a description of the evaporative emission system on your vehicle. Note that MIL means malfuntion indicator lamp.
Evaporative Emission (EVAP) Leak Check Monitor
The evaporative emission (EVAP) leak check monitor is an onboard strategy designed to detect a leak from a hole (opening) un the fuel tank and lines equal to or greater than 0.508 mm (0.020 in) in the enhanced EVAP system. The proper 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 apply 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 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.
Note: During the EVAP leak check monitor repair verification drive cycle, clearing the diagnostic trouble codes (DTCs) 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 DTCs. The EVAP leak check monitor does not run if a MAF sensor failure is indicated. The EVAP leak check monitor does not initiate until the heated oxygen sensor (HO2S) monitor has completed.
The EVAP leak check monitor is executed in 2 tests: the cruise test and the idle test. The cruise test executes when vehicle speed is above 64 km/h (40 mph). During this test the DTC P0455 is stored if a gross leak is detected, and the DTC P0422 is stored if a small leak is detected. When a very small leak is detected during this test the DTC will not be stored, however, the idle test is required to execute. The idle test starts only after a 6-hour key off soak and requires about 10 minutes to complete. The engine remains running, and the DTC P0446 is stored if the leak is present during this test. The engine returns to a normal operating mode after 10 minutes, regardless of the test result.
The EVAP leak check monitor is executed by the individual components of the enhanced EVAP system as follows:
- 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.
- The canister vent (CV) solenoid is used to seal the EVAP system from the atmosphere. It is closed by the PCM (100% duty cycle) which then allows the VMV to obtain the target vacuum on the fuel tank.
- The FTP sensor is used by the EVAP leak check monitor to determine if the target vacuum on the fuel tank is being reached to carry out the leak check. Once the target vacuum on the fuel tank is achieved, the change in fuel tank vacuum for a calibrated period of time determines if a leak exists.
- The fuel tank isolation valve (FTIV) isolates the fuel tank from the rest of the EVAP system. The FTIV allows the flow of vapors from the fuel tank to the VMV and the EVAP canister. Whenever it is desired to isolate the fuel tank from the rest of the EVAP system, the PCM provides a variable duty cycle signal (between 0% and 100%) to the solenoid which controls the FTIV operation.
- If the initial target vacuum cannot be reached, DTC P0455 (gross leak detected) is set. The EVAP leak check monitor aborts and does not continue with the leak check portion of the test.
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 is exceeded, a system flow fault exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. The EVAP leak check monitor aborts and does not continue with the leak check portion of the test.
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 0.508 mm (0.020 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 reruns the test up to 3 times.
If the bleed-up threshold is still being exceeded after 3 tests, a vapor generation check 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 VMV and opening the CV solenoid. Once the FTP sensor determines the fuel tank is at atmospheric pressure, the CV solenoid closes and seals the enhanced EVAP system.
The fuel tank pressure build-up for a calibrated period of time is compared to a calibrated threshold for pressure build-up due to vapor generation.
If the fuel tank pressure build-up exceeds the threshold, the leak test results are invalid due to vapor generation. The EVAP leak check monitor attempts to retest again.
If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 is set.
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).
If the calculated bleed-up exceeds the calibrated threshold, vapor generation is run. If vapor generation 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).
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.
If the appropriate conditions are met, a 0.508 mm (0.020 inch) leak check is conducted at idle.
If the test at idle fails, a DTC P0456 is set. There is no vapor generation test with the idle test.
Note: 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. Thereby, the test is complete for the day.
- The MIL is activated for DTCs P0442, P0455, P0456, P0457, P1450, (or P0446) after 2 occurrences of the same fault. 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, and P0453 are tested as part of the CCM.