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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 370 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0446: EVAP Vent Valve Control Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. 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, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Inspect the EVAP system for damaged EVAP vent solenoid, pinched EVAP vent hose, or damaged EVAP canister. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
  3. Turn ignition off. Disconnect the EVAP purge line from the EVAP purge solenoid. Turn ignition on, with engine off. Is the Fuel Tank Pressure Sensor parameter within -1 to 1 in. H20? If yes, go to next step. If no, go to step  10.
    4. NOTE: Do not exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
  4. Turn ignition off. Connect the EVAP purge pipe. Connect the Evaporative Emissions System Tester (J-41413-200) 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 Evaporative Emissions System Tester nitrogen/smoke supply hose to the Fuel Fill Cap Adapter. Turn ignition on, with engine off. Command the EVAP vent solenoid closed with a scan tool. Turn the nitrogen/smoke valve on the Evaporative Emissions System Tester control panel to NITROGEN. Use the remote switch to pressurize the EVAP system to 5 in. H2O. Observe the Fuel Tank Pressure Sensor parameter with a scan tool. Command the EVAP vent solenoid open with scan tool. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
  5. Command the EVAP vent solenoid ON and OFF with a scan tool. Do you hear or feel the EVAP vent solenoid click when commanded ON and OFF? If yes, go to next step. If no, go to step  8.
  6. Disconnect the EVAP vent hose from the EVAP vent solenoid. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step  12. If no, go to next step.
  7. Disconnect the EVAP vent hose from the EVAP canister. Is the Fuel Tank Pressure Sensor parameter less than 1 in. H2O? If yes, go to step  14. If no, go to step  13.
  8. Disconnect the EVAP vent solenoid. Probe the control circuit of the EVAP vent solenoid with a test light that is connected to battery voltage. Does the test light illuminate? If yes, go to next step. If no, go to step  12.
  9. Test the EVAP vent solenoid control circuit for a short to ground. Did you find and correct the condition? If yes, go to step  17. If no, go to step  11.
  10. Test for an intermittent and for a poor connection at the FTP sensor. Did you find and correct the condition? If yes, go to step  17. If no, go to step  15.
  11. Test for an intermittent and for a poor connection at the control module. Did you find and correct the condition? If yes, go to step  17. If no, go to step  16.
  12. Replace EVAP vent solenoid. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After replacing solenoid, go to step  17.
  13. Replace EVAP canister. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After replacing EVAP canister, go to step  17.
  14. Repair blockage in the EVAP vent hose. After repairs, go to step  17.
  15. Replace FTP sensor. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After replacing sensor, go to step  17.
  16. Replace PCM. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
    17. NOTE: Do not exceed the specified value in this step. Exceeding the specified value may produce incorrect test results.
  17. Turn ignition off. Connect all disconnected components. Connect the Evaporative Emissions System Tester to the fuel fill pipe. Turn ignition on, with engine off. Command the EVAP vent solenoid closed with a scan tool. Turn the nitrogen/smoke valve on the Evaporative Emissions System Tester control panel to NITROGEN. Use the remote switch to pressurize the EVAP system to 5 in. H2O. Observe the Fuel Tank Pressure Sensor parameter with a scan tool. Command the EVAP vent solenoid open with a scan tool. Is the Fuel Tank Pressure Sensor parameter less than zero in. H2O? If yes, go to next step. If no, go to step  2.
  18. Observe the stored information, Capture Info with scan tool. Does 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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