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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 385 (Engine Controls Self-Diagnostics) >> Diagnostic Tests >> DTC P0449: EVAP Vent Valve Performance >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn ignition ON, with engine OFF. With the scan tool, command the EVAP vent valve ON and OFF. Do you hear or feel a click from the EVAP vent valve when the valve is commanded ON and OFF? If yes, go to next step. If no, go to step  4.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Turn ignition ON, with engine OFF. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  4. Turn ignition OFF. Disconnect EVAP vent valve harness connector. Turn ignition ON, with engine OFF. Probe the EVAP vent valve ignition voltage circuit with a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  11.
  5. Connect a test light between the control circuit and ignition voltage circuit of the EVAP vent valve harness connector. With a scan tool, command the EVAP vent valve ON and OFF. Does the test light turn ON and OFF with each command? If yes, go to step  9. If no, go to next step.
  6. Does the test light remain illuminated with each command? If yes, go to step  8. If no, go to next step.
  7. Test the EVAP vent valve control circuit for a short to voltage or an open. Did you find and correct the condition? If yes, go to step  14. If no, go to step  10.
  8. Test the EVAP vent valve control circuit for a short to ground. Did you find and correct the condition? If yes, go to step  14. If no, go to step  10.
  9. Test for an intermittent and/or poor connections at the EVAP vent valve. Did you find and correct the condition? If yes, go to step  14. If no, go to step  12.
  10. Test for an intermittent and/or poor connections at the control module. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  11. Repair the open or short to ground in the ignition 1 voltage circuit. Did you complete the repair? If yes, go to step  14.
  12. Replace EVAP vent valve. See EVAP CANISTER VENT VALVE under SOLENOIDS in REMOVAL & INSTALLATION - CORVETTE article. Did you complete the replacement? If yes, go to step  14.
  13. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - CORVETTE article. Did you complete the replacement? If yes, go to next step.
  14. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle ? If yes, go to step  2. If no, go to next step.
  15. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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