Diagnostic Procedures
- Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
- Observe the Fuel Tank Pressure Sensor parameter on the scan tool. Remove the fuel filler cap. Is the fuel tank pressure within 0.0-0.5 in. H2O (0.0-0.9 mm Hg) with the fuel filler cap removed? If yes, go to next step. If no, go to DTC P0451: FUEL TANK PRESSURE SENSOR PERFORMANCE .
- Turn OFF the ignition. Disconnect the electrical connector from the EVAP canister vent valve. Measure the resistance of the EVAP canister vent valve using a Digital Multimeter (DMM). Is the resistance within the specified range of 28-36 ohms at 68°F (20°C)? If yes, go to next step. If no, go to step 11 .
- Turn ON the ignition, leaving the engine OFF. Probe the ignition positive voltage circuit at the vent valve electrical connector with a test light connected to ground. Does the test light illuminate? If yes, go to next step. If no, go to step 7 .
- Connect the electrical connector to the EVAP canister vent valve. Clear the DTCs with a scan tool. Backprobe the vent valve control circuit with a test light connected to B+. Command the vent valve ON and OFF with the scan tool. Does the test light illuminate only when commanded ON with the scan tool? If yes, go to step 8 . If no, go to next step.
- Check for an open or a short in the vent valve control circuit. Repair as necessary. Was a repair necessary? If yes, go to step 13 . If no, go to step 12 .
- Check for an open in the ignition positive voltage circuit. Repair as necessary. After repairs, go to step 13 .
- Check the EVAP vent valve inlet air filter and line for blockage. Was a repair necessary? If yes, go to step 13 . If no, go to next step.
- Check the EVAP canister for restrictions or blockages. Did the canister pass all tests? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
- Replace the EVAP canister. After repairs, go to step 13 .
- Replace the EVAP canister vent valve. After repairs, go to step 13 .
- Turn ignition off. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After replacing PCM, go to next step.
- Turn OFF the ignition. Remove the DOME fuse for 30 seconds. Install the DOME fuse. Reset the radio clock time. Start the engine. Operate the vehicle within the Conditions for Running the DTC or until the DTC P0446 diagnostic test has run. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step 2 .
- Using scan tool, observe stored information and Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.