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:
- 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.
- 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 EVAP canister purge valve to obtain the target vacuum on the fuel tank.
- The FTP sensor will be 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 will determine if a leak exists.
- If the initial target vacuum cannot be reached, DTC P0455 (gross leak detected) will be set. The engine on EVAP leak check monitor will abort and 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.
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 engine on EVAP leak check monitor will abort and 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) will be calculated for a calibrated period of time. The calculated change in fuel tank vacuum will be 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 will abort and rerun the test up to 3 times.
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) will be 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.
The fuel tank pressure build-up, over a calibrated period of time will be 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 engine on EVAP leak check monitor will attempt to retest again.
If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 will be set.
- 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.
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, 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).
On the next start following a long engine off period, the enhanced EVAP system will be 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 will be 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, P1443, and 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, P0453, and P1451 are tested as part of the CCM.