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Home >> Chevrolet >> 1998 >> Astro Van Cargo, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0446 - EVAP System Vent Valve Performance >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . Retrieve and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. After performing OBD system check, go to next step.
  2. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, read FUEL TANK PRESSURE. If scan tool displays zero in. H2O, go to next step. If scan tool does not display zero in. H2O, perform fuel tank sensor circuit diagnosis. See BASIC TESTING article.
  3. Zero pressure and vacuum gauges on EVAP Pressure/Purge Diagnostic Station (J 41413). Reinstall fuel cap. Using scan tool, command EVAP vent solenoid ON (closed). Connect EVAP pressure/purge diagnostic station to EVAP service port. Using EVAP pressure/purge diagnostic station, pressurize EVAP system to 5 in. H2O. Using scan tool, read FUEL TANK VACUUM. If scan tool displays 5 in. H2O, go to next step. If scan tool does not display 5 in. H2O, repair faulty fuel tank sensor circuit.
  4. Maintain EVAP system pressure at 5 in. H2O. Using scan tool, command EVAP vent solenoid OFF (open). Monitor EVAP pressure/purge diagnostic station pressure gauge. If pressure decreases to zero in H2O within 5 seconds, see DIAGNOSTIC AIDS. If pressure does not decrease as specified, go to next step.
  5. Disconnect vent and fuel tank vapor hose from EVAP canister. Plug fuel tank vapor line fitting at EVAP canister. Switch EVAP pressure/purge diagnostic station rotary switch to RELEASE position. Connect a hand-held vacuum pump to EVAP purge line fitting on EVAP canister. Apply 5 in. Hg. If specified vacuum can be obtained, go to step 11). If specified vacuum cannot be obtained, go to next step.
  6. Check if vent hose is between EVAP canister and EVAP solenoid is kinked, pinched or blocked. If a problem is found, repair as necessary. After repairs, go to step 13). If no problem is found, go to next step.
  7. Turn ignition off. Disconnect vent valve harness connector. Turn ignition on, engine off. Using a test light connected to battery voltage, probe harness connector terminal "A". If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
  8. Turn ignition off. Disconnect VCM harness connector. Connect test light between battery voltage and EVAP vent valve harness connector terminal "A". If test light does not illuminate, go to next step. If test light does not illuminate, go to step 12).
  9. Repair short to ground in EVAP vent valve control circuit. After repairs, go to step 13).
  10. Replace EVAP vent valve. After replacing valve, go to step 13).
  11. Replace EVAP canister. After replacing canister, go to step 13).
  12. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
  13. Using scan tool, command EVAP vent solenoid ON (closed). With EVAP pressure/purge diagnostic station connected to EVAP service port, pressurize EVAP system to 5 in. H2O. Switch EVAP pressure/purge diagnostic station rotary switch to HOLD. Using scan tool, command EVAP vent solenoid OFF (open). If pressure decreases to zero in H2O within 5 seconds, go to next step. If pressure does not decrease as specified, repeat step 2).
  14. Using scan tool, select DTC and CLEAR DTC INFO functions. Clear DTCs. Perform EVAP SERVICE BAY TEST. After performing service bay test, go to next step.
  15. Check if additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are set, system is okay.
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