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 (P0452, P0453), EVAP purge solenoid (Must review Failure Record to determine if the EVAP purge solenoid circuit had faulted. A YES on Scan tool would be indicated for EVAP PURGE CKT OPEN SHORT TO GND or EVAP PURGE CKT SHORT TO VOLTS); or EVAP vent solenoid (Must review Failure Record to determine if the EVAP vent solenoid circuit had faulted. A YES on Scan tool would be indicated for EVAP VENT CKT OPEN SHORT TO GND or EVAP VENT CKT SHORT TO VOLTS) 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 2.35 to 2.85 volts.
4. Reinstall fuel cap.
5. If DTC P0446 or P1441 is set, diagnose that DTC next.
6. If DTC P0440 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.