Engine On EVAP Leak Check Monitor - Fiesta
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The engine on EVAP leak check monitor is executed by the individual components of the enhanced EVAP system as follows:
- The PCM uses inputs from the engine coolant temperature (ECT) sensor, the fuel level input (FLI), the intake air temperature (IAT) sensor, the mass airflow (MAF) sensor, the NVLD ambient air temperature sensor, the vehicle speed sensor (VSS) and the NVLD module to determine conditions of the enhanced EVAP system. The combination of these signals are used by the PCM to determine when to activate the EVAP leak check monitors.
- The fuel tank pressure is inferred by the PCM based on a message from the NVLD module and other engine parameters. The NVLD module message is based on the position of the NVLD vacuum switch and the NVLD ambient air temperature sensor during calibrated conditions of the EVAP system.
- The EVAP canister purge valve creates a vacuum in the fuel tank for the large leak check. In order to detect if the canister purge valve will open and allow the vacuum to be released, a canister purge valve check is initiated after the NVLD vacuum switch is detected as closed.
- The NVLD module uses the NVLD vacuum switch to seal the EVAP system from the atmosphere. The NVLD vacuum switch is closed when a vacuum is created in the fuel tank. The NVLD vacuum switch position is monitored for correct operation after the NVLD vacuum switch is detected as closed. Correct operation of the NVLD vacuum switch is determined by opening the canister purge valve with the engine OFF to relieve the vacuum in the fuel tank and force the NVLD vacuum switch to open. If the NVLD vacuum switch does not open within a calibrated amount of time, a mechanical switch error is detected.
- If the NVLD vacuum switch is closed at the beginning of the large leak test, then the EVAP system does not have a large leak and the test is passed.
- If the NVLD vacuum switch is open at the beginning of the large leak test, the PCM opens the EVAP canister purge valve to a calibrated amount creating a vacuum in the fuel tank. The NVLD vacuum switch position is monitored by the NVLD module. If the NVLD vacuum switch closes within a calibrated period of time after the EVAP canister purge valve is open, the system does not have a large leak and the test is passed.
- On a normally operating EVAP system, a vacuum is generated inside the fuel tank as the temperature of the fuel decreases.