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Home >> Buick >> 2001 >> Century Limited >> Repair and Diagnosis (Single Page) >> Engine Performance >> Testing & Diagnosis >> Engine Controls Self-Diagnostics - 3.1L & 3.4L >> Diagnostic Tests >> DTC P0446: EVAP Canister Vent Blocked >> Diagnostic Procedure

Diagnostic Procedure

  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 DTC P0443, P0449, or P0453 are set, diagnose affected DTC first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If DTC P0443, P0449, or P0453 are not set, go to next step.
  3. Inspect EVAP vent valve for damage. Check for pinched EVAP vent hose. For component locations, see VACUUM DIAGRAMS - CARS article. If a problem is found, repair as necessary, then go to step  14. If no problems were found, go to next step.
  4. Disconnect purge line from EVAP canister purge valve. Turn ignition on. Using scan tool, observe Fuel Tank Pressure (FTP) parameter. If scan tool displays zero in. H2O, go to next step. If scan tool does not display zero in. H2O, go to step  8.
    5. NOTE: To avoid incorrect test results, do not pressurize EVAP system with more than 5 in. H2O.
  5. Turn ignition off. Reconnect all previously disconnected components. Install Fuel Fill Cap Adapter (J 41415). Connect EVAP Pressure and Purge Station (J 41413) and fuel fill cap to fuel fill cap adapter. Turn ignition on. Using scan tool, command EVAP canister vent valve on. Using EVAP pressure and purge station, pressurize EVAP system to 5 in. H2O. Turn rotary switch on pressure and purge station to OFF/HOLD position. Using scan tool, command EVAP canister vent valve off. If scan tool indicates that FTP is about zero in. H2O, go to step  10. If scan tool does not indicate that FTP is about zero in. H2O, go to step  7.
  6. Disconnect EVAP canister vent hose from EVAP canister vent valve. If scan tool indicates that FTP is -0.5 in. H2O to +0.5 in. H2O, go to step  10. If scan tool does not indicate that FTP is -0.5 in. H2O to +0.5 in. H2O, go to next step.
  7. Disconnect EVAP vent pipe from EVAP canister. If scan tool indicates that FTP is about zero in. H2O, go to step  13. If scan tool does not indicate that FTP is about zero in. H2O, go to step  11.
  8. Using scan tool, observe FTP sensor voltage. If scan tool displays more than 4.3 volts, see DTC P0453: FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE . If scan tool does not display more than 4.3 volts, go to next step.
  9. Inspect FTP sensor harness connector for poor connections. On Alero, Grand Am and Malibu, fuel tank must be removed for access to FTP sensor harness connector. On all other models, remove fuel sender access panel located under trunk liner. On all models, repair connector as necessary, then go to step  14. If connector is okay, go to step  12.
  10. Replace EVAP canister vent valve. After repairs, go to step  14.
  11. Replace EVAP canister. After repairs, go to step  14.
  12. Replace FTP sensor. After repairs, go to step  14.
  13. Repair blockage in EVAP vent hose. After repairs, go to next step.
  14. Turn ignition on. Using scan tool, command EVAP canister vent valve on. Using EVAP pressure and purge station, pressurize EVAP system to 5 in. H2O. Turn rotary switch on pressure and purge station to OFF/HOLD position. Monitor pressure gauge on EVAP pressure and purge station. Using scan tool, command EVAP canister vent valve off. If pressure decreases, go to next step. If pressure does not decrease, go to step  3.
  15. Using scan tool, observe all stored information. If scan tool displays any DTCs that have not been diagnosed, diagnose those DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If scan tool does not display any DTCs, system is okay.
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