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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 51 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0446: EVAP Vent Valve Performance >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 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. Did DTCs P0452 or P0453 also set? If yes, see DTC P0452: FUEL TANK PRESSURE SENSOR - LOW VOLTAGE  or DTC P0453: FUEL TANK PRESSURE SENSOR - HIGH VOLTAGE  . If no, go to next step.
  3. Inspect the EVAP system for the following conditions:
    • A damaged EVAP vent valve.
    • A pinched EVAP vent hose.

    Did you find and correct the condition? If yes, go to step  19 . If no, go to next step.

  4. Install the J 41415-40 Fuel Tank Cap Adapter to the fuel filler neck. Install the J 41413 EVAP Pressure/Purge Diagnostic Station and the fuel tank cap to the adapter. Turn ON the ignition, with the engine OFF. Command the EVAP vent valve ON (closed) with a scan tool. With the EVAP diagnostic station, pressurize the EVAP system to 13 in. H2O. Rotate the EVAP pressure/purge diagnostic station rotary switch to the OFF/HOLD position. Using the scan tool, compare the Fuel Tank Pressure (FTP) sensor value to the EVAP pressure/purge diagnostic station gage value. Are the EVAP pressure/purge diagnostic station gage and the scan tool FTP sensor values similar? If yes, go to next step. If no, go to step  9 .
  5. Monitor the EVAP pressure/purge diagnostic station gage. Command the EVAP canister vent valve OFF or open. Did the EVAP pressure/purge diagnostic station gage drop quickly to near 0 in. H2O? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to next step.
  6. Command the EVAP vent valve ON and OFF with a scan tool. Do you hear or feel the EVAP vent valve click when commanded ON and OFF? If yes, go to next step. If no, go to step  10 .
  7. Turn OFF the ignition. Connect all previously disconnected hardware. With the EVAP pressure/purge diagnostic station, pressurize the EVAP system to 13 in. H2O. Rotate the EVAP pressure/purge diagnostic station rotary switch to the OFF/HOLD position. Disconnect the EVAP vent hose from the EVAP vent valve. Does the scan tool indicate fuel tank pressure near 0 in. H2O? If yes, go to step  14 . If no, go to next step.
  8. Disconnect the EVAP vent hose from the EVAP canister. Does the scan tool indicate fuel tank pressure near 0 in. H2O? If yes, go to step  16 . If no, go to step  15 .
  9. Is the FTP sensor value more than 4.3 V? If yes, see DTC P0453: FUEL TANK PRESSURE SENSOR - HIGH VOLTAGE  . If no, go to step  12 .
  10. Disconnect the EVAP vent valve harness connector. Probe the EVAP vent valve control circuit with a test light connected to battery voltage. Does the test light illuminate? If yes, go to next step. If no, go to step  14 .
  11. Test the control circuit of the EVAP vent valve for a short to ground. Did you find and correct the condition? If yes, go to step  19 . If no, go to step  13 .
  12. Test for poor connections at the harness connector of the FTP. Did you find and correct the condition? If yes, go to step  19 . If no, go to step  17 .
  13. Test for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step  19 . If no, go to step  18 .
  14. Replace the EVAP vent valve. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  19 .
  15. Replace the EVAP canister. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  19 .
  16. Repair the blockage in the EVAP vent hose. After repairs, go to step  19 .
  17. Replace the FTP sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  19 .
  18. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  19. Connect all of the EVAP hardware that was previously disconnected. Turn ON the ignition, with the engine OFF. Command the EVAP canister vent valve ON or closed with a scan tool. With the EVAP pressure/purge diagnostic station, pressurize the EVAP system to 13 in. H2O. Rotate the EVAP pressure/purge diagnostic station rotary switch to the OFF/HOLD position. Command the EVAP canister vent valve OFF (open). Is the EVAP pressure/purge diagnostic station value near 0 in. H2O? If yes, go to next step. If no, go to step  3 .
  20. Observe the stored information, Capture Info with a scan tool. 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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