Diagnosing A Fault In the EVAP System

When the MIL is commanded On and an EVAP DTC is set, there are certain ordered steps that should be taken to ensure correct diagnosis.

IMPORTANT: If any of the above DTCs are set, the ECM will NOT run the EVAP diagnostic leak test.

1. Diagnose any hard circuit fault fuel tank pressure (P0451, P0452 or P0453), EVAP purge solenoid (P0443, P0444 or P0445); or EVAP vent solenoid (P0447, P0448 or P0449)
2. Using Scan tool, monitor FUEL TANK PRESS. SENSOR with the ignition On, engine Off and fuel cap removed. The voltage should be between 2.35 to 2.85 volts.
3. Reinstall fuel cap.
4. If DTC P0440 or P446 is set, diagnose that DTC next.
5. If DTC P0455 or P0442 is set, diagnose that DTC next. A leak in the system must be present, if one of these two DTCs are set. Use the EVAP PRESSURE/PURGE DIAGNOSTIC CART TEST PROCEDURE to locate the leak.