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 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 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. 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 vapor vent valve isolates the fuel tank from the rest of the EVAP system. The fuel vapor vent valve allows the flow of vapors from the fuel tank to the EVAP canister purge valve and the EVAP canister. Whenever it is desired to isolate the fuel tank from the rest of the EVAP system, the PCM provides a duty cycle signal of 100% to command the valve closed. To allow flow of fuel vapors from the fuel tank, the PCM provides 0% duty cycle and the fuel vapor vent valve opens.
- 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 concern 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.
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.
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 three times.
If the bleed-up threshold is still being exceeded after three 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.
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.
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.
If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 is set.
If DTC P0442 is set and the functional test completes without a fault, a functional test of the fuel vapor vent valve is performed to determine if the valve is stuck open. If the valve is stuck open, DTC P2450 is set. Additionally a circuit test of the fuel vapor vent valve is performed continuously. If the circuit test fails, DTC P2418 is set.
- The malfunction indicator lamp (MIL) is activated for DTCs P0442, P0455, P0456, P0457, and P1450 after two occurrences of the same concern and for DTC P144A or P2450 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, P0446, P0452, P0453, and P2418 are tested as part of the comprehensive component monitor (CCM).