Evaporative Emission (EVAP) Leak Check Monitor: Notes

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The EVAP leak check monitor is an on board strategy designed to detect a leak from an opening equal to or greater than 0.5 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 (if equipped), intake air temperature (IAT) sensor, mass airflow (MAF) sensor (if equipped), 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 continuous diagnostic trouble codes (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 ignition is turned OFF after clearing the continuous DTCs and resetting the emission monitors information in the PCM. 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.