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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P0449: EVAP Vent Valve Performance >> Diagnostic Procedures

Diagnostic Procedures

  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. Review the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observe. See CONDITIONS FOR RUNNING DTC . Does this DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article.
  4. Turn ignition off. Disconnect the EVAP vent valve harness connector. Turn ignition on, with engine off. Probe the ignition voltage circuit of the EVAP vent valve 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 control circuit of the EVAP vent valve 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 control circuit of the EVAP vent valve 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. Inspect for poor connections at the harness connector of the EVAP vent valve. Did you find and correct the condition? If yes, go to step  14. If no, go to step  12.
  10. Inspect for poor connections at the harness connector of the control module. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
    11. NOTE: If the fuse is open, inspect all related circuits for a short to ground.
  11. Repair the ignition voltage circuit of the EVAP vent valve for an open or a short to ground. After repairs, go to step  14.
  12. Replace EVAP vent valve. After repairs, go to step  14.
  13. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  14. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  15. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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