Diagnostic Aids

ECM using an in-tank pressure sensor monitors pressure build-up to determine whether leaks are present. Possible reasons for a detected leak are:

• Fuel filler cap is not properly tightened or is missing.
• There is an in-tank pressure sensor or actuator open circuit.
• There is a short to battery voltage or ground.
• Either purge or CVS valve is stuck open.
• Either purge or CVS valve is stuck closed or there is a blocked line.
• There is a loose, leaking, broken or disconnected EVAP system line.

If the EVAP system line is broken forward of the purge valve or is not connected, the engine may run rough and fueling adaptations will drift. The malfunction will not be detected by the ECM leak test, but by the ECM detection of a suspended fueling adaptation. The evaluation of EVAP system leakage is dependent on the differential pressure between fuel tank and ambient atmospheric pressure. The leak test is disabled at altitudes greater than 9500 feet.

If ECM detects a EVAP system leak, the following DTCs may be set:

1. If DTC P0442 is set, a small leak has been detected within the EVAP system.
2. If DTC P0455 is set, a large leak has been detected within the EVAP system.