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Home >> Buick >> 2001 >> Regal LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0440: EVAP System >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
  2. If scan tool indicates DTCs P0443 or P0449 are also set, diagnose these codes first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If scan tool does not indicate DTCs P0443 or P0449 are set, go to next step.
  3. Inspect EVAP system for the following conditions:
    • Loose, missing, or damaged service port Schrader valve.
    • Loose, incorrect, missing, or damaged fuel fill cap.
    • Damaged EVAP canister purge valve.
    • Disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses.
    • Damaged EVAP canister vent valve or EVAP canister.

    If problem was found, repair as necessary. After repairs, go to step  18. If problem was not found, go to next step.

    4. NOTE: Always zero EVAP pressure and vacuum (in. H2O) gauges on EVAP pressure and purge station before proceeding with diagnosis.
  4. Install Fuel Tank Cap Adapter (J 41415-40). Connect EVAP Pressure and Purge Station (J 41413) and vehicle fuel fill cap to fuel tank cap adapter. Turn ignition on, engine off. Using scan tool, seal EVAP system. Using EVAP pressure and purge station, pressurize system to 5 in. H2O. Rotate EVAP pressure and purge station rotary switch to OFF/HOLD position. Monitor pressure gauge for one minute. If 5 in. H2O was obtained and held, go to next step. If 5 in. H2O was not obtained and held, go to step  7.
  5. Compare EVAP pressure and purge station value to scan tool FTP sensor value. If EVAP pressure and purge station value measure about scan tool value, go to next step. If EVAP pressure and purge station value do not measure about scan tool value, go to step  11.
  6. Monitor pressure gauge on EVAP pressure and purge station. Disconnect EVAP purge pipe from EVAP purge valve. If EVAP system pressure decreases, go to step  8. If EVAP system pressure does not decrease, go to step  9.
    7. NOTE: Fuel tank may need to be partially lowered to inspect components located in upper portion of tank.
  7. Using EVAP pressure and purge station, continuously pressurize EVAP system. Using Ultrasonic Leak Detector (J 41416), inspect for leaks in the following locations:
    • EVAP system purge pipe.
    • EVAP vapor pipe.
    • EVAP vent hose/pipe.
    • Fuel fill pipe/hose and fuel fill cap.
    • EVAP canister.
    • EVAP canister vent valve.
    • EVAP canister purge valve.
    • Fuel sender assembly and/or seal.
    • FTP sensor seal.
    • Fill limiter vent valve, pressure relief valve, rollover valve, or fuel tank.

    If problem was found, repair as necessary. After repairs, go to step  18. If problem was not found, see DIAGNOSTIC AIDS .

  8. Attach a vacuum gauge to EVAP purge valve purge pipe port. Start engine and allow engine to idle. Using scan tool, command EVAP purge valve to 50 percent. If vacuum gauge shows vacuum more than 10 in. H2O, see DIAGNOSTIC AIDS . If vacuum gauge does not show vacuum more than 10 in. H2O, go to step  12.
  9. Monitor pressure gauge on EVAP pressure and purge station. Disconnect EVAP purge pipe from EVAP canister. If EVAP system pressure decreases, go to step  14. If EVAP system pressure does not decrease, go to next step.
  10. Monitor pressure gauge on EVAP pressure and purge station. Disconnect EVAP purge pipe from EVAP purge valve. If EVAP system pressure decreases, go to step  17. If EVAP system pressure does not decrease, go to step  13.
  11. Using scan tool, monitor FTP sensor voltage. If FTP sensor voltage is more than 4.3 volts, see DTC P0453: FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE . If FTP sensor voltage is not more than 4.3 volts, go to step  15.
  12. Check vacuum source to EVAP purge valve for blockage, cuts, or disconnects. If problem was found, repair as necessary. After repairs, go to step  18. If problem was not found, go to step  16.
  13. Repair pinched or obstructed EVAP vapor pipe. After repairs, go to step  18.
  14. Repair restriction in EVAP purge pipe. After repairs, go to step  18.
  15. Replace FTP sensor. After repairs, go to step  18.
  16. Replace EVAP purge valve. After repairs, go to step  18.
  17. Replace EVAP canister. After repairs, go to step  18.
    18. NOTE: DO NOT exceed specified value in this step. Exceeding specified value may produce incorrect test results.
  18. Turn ignition on, engine off. Using scan tool, command EVAP canister vent valve on. Using EVAP pressure and purge station, pressurize EVAP system to 5 in. H2O. Place control knob on EVAP pressure and purge station to OFF/HOLD position. Monitor EVAP system pressure on EVAP pressure and purge station for 5 minutes. If EVAP system pressure remains constant, go to next step. If EVAP system pressure does not remain constant, go to step  7.
  19. Monitor pressure gauge on EVAP pressure and purge station. Using scan tool, command EVAP purge valve to 50 percent. If EVAP system pressure decreases, go to next step. If EVAP system pressure does not decrease, go to step  9.
  20. Using scan tool, observe stored information. If scan tool displays any DTCs that have not been diagnosed, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If scan tool does not display any DTCs, system is okay.
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