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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 28 (Engine Control System - Self-Diagnostics) >> Diagnostic Tests >> DTC P0446: EVAP Vent System Performance >> Diagnostic Procedures
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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Pontiac Vibe. 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, perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Install scan tool and check for DTCs. Is a DTC P0450 or P0451 present? If yes, go to DTC P0450: FUEL TANK PRESSURE SENSOR CIRCUIT  or DTC P0451: FUEL TANK PRESSURE SENSOR PERFORMANCE . If no, go to next step.
  3. Review freeze frame/failure records. Diagnose DTC captured in freeze frame/failure records first. Is DTC P0446 captured in freeze frame/failure records? If yes, go to next step. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  4. Using scan tool, command EVAP vent solenoid ON and OFF. Do you hear or feel a click as EVAP vent solenoid is commanded ON and OFF? If yes, go to next step. If no, go to step  11.
  5. Using scan tool, command EVAP pressure switching solenoid ON and OFF. Do you hear or feel a click as EVAP pressure switching solenoid is commanded ON and OFF? If yes, go to next step. If no, go to step  13.
  6. Remove fuel fill cap to release any pressure inside fuel tank. Re-install fuel fill cap. Turn ignition switch to RUN position, engine OFF. Observe FTP sensor parameter on scan tool. Is FTP sensor 0.09 in. H2O? If yes, go to next step. If no, go to step  20.
  7. Disconnect EVAP solenoid vent hose at the EVAP canister. Command EVAP vent solenoid ON (closed). Install a vacuum pump to vent hose and apply a vacuum. Did you achieve a vacuum? If yes, go to next step. If no, go to step  22.
  8. Command EVAP vent solenoid OFF (open). If yes, go to next step. If no, go to step  23.
  9. Disconnect EVAP pressure switching solenoid hose from one of the ports. Command EVAP pressure switching solenoid OFF (closed). Install a vacuum pump to the solenoid port and apply a vacuum. Did you achieve a vacuum? If yes, go to next step. If no, go to step  25.
  10. Command EVAP pressure switching ON (open). Does the vacuum decrease? If yes, go to step  28. If no, go to step  25.
  11. Turn ignition switch to RUN position, engine OFF. Disconnect EVAP vent solenoid. Connect a test light between EVAP vent solenoid ignition positive voltage circuit and a known-good ground. Does test light illuminate? If yes, go to next step. If no, go to step  17.
  12. Connect test light between EVAP vent solenoid ignition positive voltage circuit and control circuit. Using scan tool, command EVAP vent solenoid ON. Does test light illuminate when EVAP vent solenoid is commanded ON and turn OFF when EVAP vent solenoid is commanded OFF? If yes, go to step  18. If no, go to step  15.
  13. Turn ignition switch to RUN position, engine OFF. Disconnect EVAP pressure switching solenoid. Connect test light between EVAP pressure switching solenoid ignition positive voltage circuit and a known-good ground. Does test light illuminate? If yes, go to next step. If no, go to step  17.
  14. Connect test light between EVAP pressure switching solenoid ignition positive voltage circuit and control circuit. Using scan tool, command EVAP pressure switching solenoid ON. Does test light illuminate when EVAP pressure switching solenoid is commanded ON and turn OFF when EVAP pressure switching solenoid is commanded OFF? If yes, go to step  19. If no, go to step  16.
  15. Check EVAP vent solenoid control circuit for an open, short to ground, or a short to voltage. Did you find and correct the condition? If yes, go to step  28. If no, go to step  21.
  16. Check EVAP pressure switching solenoid control circuit for an open, a short to ground, or for a short to voltage. Did you find and correct the condition? If yes, go to step  28. If no, go to step  21.
  17. Repair open or short to ground in EVAP solenoid ignition positive voltage circuit. Replace fuse as necessary. After repair, go to step  28.
  18. Check EVAP canister vent solenoid for an intermittent and for a poor connection. Did you find and correct the condition? If yes, go to step  28. If no, go to step  24.
  19. Check EVAP pressure switching solenoid for an intermittent and for a poor connection. Did you find and correct the condition? If yes, go to step  28. If no, go to step  26.
  20. Check FTP sensor for an intermittent and for a poor connection. Did you find and correct the condition? If yes, go to step  28. If no, go to step  26.
  21. Check PCM for an intermittent and for a poor connections. Did you find and correct the condition? If yes, go to step  28. If no, go to step  27.
  22. Check for a leak source in EVAP solenoid vent hose. Repair as necessary Did you find and correct the condition? If yes, go to step  28. If no, go to step  24.
  23. Check EVAP solenoid vent hose for a blockage or restriction. Repair as necessary. Did you find and correct the condition? If yes, go to step  28. If no, go to step  24.
  24. Replace EVAP vent solenoid. After repair, go to step  28.
  25. Replace EVAP pressure switching solenoid. After repair, go to step  28.
  26. Replace FTP sensor. After repair, go to step  28.
  27. Replace PCM. After repair, go to next step.
  28. Start engine. Select EVAP PURGE SEAL function on scan tool. Command EVAP PURGE SEAL function ON. Does FTP sensor indicate a reading of -12.50 in. H2O for as long as 2 minutes? If yes, go to next step. If no, go to step  4.
  29. With a scan tool, observe stored information, CAPTURE INFO. Does scan tool display any DTCs that have not been diagnosed? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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