LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Buick >> 2003 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 3.1L Engine >> Diagnostic Tests >> DTC P0446: EVAP Vent System Performance >> Diagnostic Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedure

  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. Observe the Freeze Frame/Failure Records for this DTC. Perform the Service Bay Test. Go to SERVICE BAY TEST  under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
  3. Check the EVAP system for the following conditions:
    • A damaged EVAP vent solenoid.
    • A pinched EVAP vent hose.
    • A damaged EVAP canister.

    Did you find and correct the condition? If yes, go to step  13. If no, go to next step.

  4. Turn ignition switch to OFF position. Disconnect the purge line from the EVAP purge solenoid. Turn ignition switch to RUN position, engine OFF. Is the Fuel Tank Pressure (FTP) sensor parameter -1 to 1 in. H2O? If yes, go to next step. If no, go to step  9.
    5. NOTE: Do not exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
  5. Turn ignition switch to OFF position. Connect the EVAP purge pipe. Connect the Evaporative Emissions System Tester (EEST) (J 41413-200), or equivalent, power supply clips to a known good 12-volt source. Install the Fuel Fill Cap Adapter (J 41415-40) to the fuel fill pipe. Connect the fuel fill cap to the fuel fill cap adapter. Connect the EEST nitrogen/smoke supply hose to the fuel fill cap adapter. Turn ignition switch to RUN position, engine OFF. Command the EVAP vent solenoid closed using a scan tool. Turn the nitrogen/smoke valve on the EEST control panel to NITROGEN. Use the remote switch to pressurize the EVAP system to 5 in. H2O. Observe the FTP sensor parameter using a scan tool. Command the EVAP vent solenoid open. Is the FTP Sensor parameter less than 1 in. H2O? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
  6. Disconnect the EVAP vent hose from the EVAP vent solenoid. Is the FTP sensor parameter less than 1 in. H2O? If yes, go to step  11. If no, go to next step.
  7. Disconnect the EVAP vent hose from the EVAP canister. Is the FTP sensor parameter less than 1 in. H2O? If yes, go to next step. If no, go to step  12.
  8. Repair the pinched or restricted EVAP vent hose. After repair, go to step  13.
  9. Test for an intermittent and for a poor connection at the Powertrain Control Module (PCM). Did you find and correct the condition? If yes, go to  13. If no, go to next step.
  10. Replace the FTP sensor. After repair, go to step  13.
  11. Replace the EVAP vent solenoid. After repair, go to step  13.
  12. Replace the EVAP canister. After repair, go to next step.
  13. Perform the Service Bay Test. Go to SERVICE BAY TEST  under DRIVE CYCLES. Does the scan tool indicate that the service bay test passed? If yes, go to next step. If no, go to step  3.
  14. Using the scan tool, observe the stored information in 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 at this time.
scientia non olet · About LEMON Manuals