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.
1. Diagnose any hard circuit fault fuel tank pressure sensor (P0452 or P0453), EVAP purge solenoid (P0444 or P0445) or EVAP vent solenoid (P0447 or P0448) DTCs first. These types of DTCs are probably the cause of other non-hard circuit fault EVAP DTCs.
2. Make sure the fuel level is between 15% and 85% and fuel gauge reads correctly.
3. Using Scan tool, monitor FUEL TANK PRESS. SENSOR with the ignition On, engine Off and fuel cap removed. The voltage should be between 1.3 to 1.7 volts.
4. Reinstall fuel cap.
5. Using Scan tool, perform the EVAP SERVICE BAY TEST to verify the system has failed. If DTC P0446 or P1441 set, diagnose that DTC. If the EVAP SERVICE BAY TEST passed, refer to the Diagnostic Aids section of the initial individual DTC that set to help locate a problem.
6. A leak in the system must be present, if the EVAP SERVICE BAY TEST failed. The test is the same test the PCM performs in the previous flowchart, however, the enable criteria is by-passed. Use the EVAP PRESSURE/PURGE DIAGNOSTIC CART TEST PROCEDURE to locate the leak.