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Home >> Buick >> 2002 >> Century Custom >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.1L Engine >> Diagnostic Tests >> DTC P0440: EVAP System >> Diagnostic Procedures
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Diagnostic Procedures

  1. 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.
  2. Does the scan tool indicate DTC P0443 or P0449 are also set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Inspect the EVAP system for loose, missing, or damaged service port Schrader valve. For loose, incorrect, missing or damaged fuel fill cap, or a damaged EVAP canister purge valve. Raise vehicle on a hoist. Inspect EVAP system for disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses, a damaged EVAP canister vent valve or EVAP canister. Did you find and correct the condition? If yes, go to step  19. If no, go to next step.
  4. With a scan tool, capture and record the Fail Record data and clear the DTCs. Perform the Service Bay Test. Does the scan tool indicate that the Service Bay Test passed? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
    NOTE: Always zero the EVAP Pressure and vacuum (in. H2O) gauges on EVAP Pressure and Purge Station before proceeding with diagnosis.
  5. Install the J-41415-40 Fuel Tank Cap Adaptor. Connect the J-41413 EVAP Pressure and Purge Station and the vehicle fuel fill cap to the J-41415-40. Turn ignition on, with engine off. Seal the EVAP system with the scan tool. Pressurize the system to 5 in. H2O with the J-41413. Rotate the J-41413 rotary switch to the OFF/HOLD position. Monitor the pressure gauge for 1 minute. Did you obtain and hold the pressure? If yes, go to next step. If no, go to step  8.
  6. Compare the J-41413 value to the scan tool Fuel Tank Pressure (FTP) sensor value. Does J-41413 value measure near the scan tool value? If yes, go to next step. If no, go to step  12.
  7. Monitor the pressure gauge on the J-41413. Disconnect the EVAP purge pipe from the EVAP purge valve. Does the EVAP system pressure decrease? If yes, go to step  9. If no, go to step  10.
  8. Continuously pressurize the EVAP system with the J-41413. The fuel tank may need to be partially lowered to inspect components located in the upper portion of the tank. Inspect for leaks using J-41416 Ultrasonic Leak Detector at the EVAP system purge pipe, EVAP vapor pipe, EVAP vent hose/pipe, fuel fill pipe/hose, 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 valves, and/or fuel tank. Did you find and repair a leak? If yes, go to step  19. If no, go to DIAGNOSTIC AIDS .
  9. Attach a vacuum gauge to the purge pipe port of the EVAP purge valve. Start engine and allow the engine to idle. Command the EVAP purge valve to 50 percent with a scan tool. Does the vacuum gauge show vacuum more than 10 in. H2O. If yes, go to DIAGNOSTIC AIDS . If no, go to step  13.
  10. Monitor the pressure gauge on the J-41413. Disconnect the purge pipe at the EVAP canister. Does the EVAP system pressure decrease? If yes, go to step  15. If no, go to next step.
  11. Monitor the pressure gauge on the J-41413. Disconnect the EVAP vapor line from the EVAP canister. Does the EVAP system pressure decrease? If yes, go to step  18. If no, go to step  14.
  12. Monitor the FTP sensor voltage with a scan tool. Is the FTP sensor voltage more than 4.3 volts? If yes, go to DTC P0453: FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE . If no, go to step  16.
  13. Inspect the vacuum source to the EVAP purge valve for blockage, cuts, or disconnects. Repair as necessary. Did you find and correct the condition? If yes, go to step  19. If no, go to step  17.
  14. Repair the pinched or obstructed EVAP vapor pipe. After repairs, go to step  19.
  15. Repair the restriction in the EVAP purge pipe. After repairs, go to step  19
  16. Replace the FTP sensor. After repairs, go to step  19.
  17. Replace the EVAP purge valve. After repairs, go to step  19.
  18. Replace the EVAP canister. After repairs, go to next  19.
  19. With a scan tool, capture and record the Fail Record data and clear the DTCs. Perform the Service Bay Test. Does the scan tool indicate that the Service Bay Test passed? If yes, go to next step. If no, go to step  5.
  20. Using scan tool, observe stored information and Capture Info. 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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