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Home >> Chevrolet >> 1998 >> Forward Control P30, 6.5 F, Standard >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 3 (Engine Controls - Tests W/Codes - 5.7L) >> Diagnostic Trouble Codes >> DTC P0446 - EVAP Canister Vent Valve Performance >> Diagnostic Procedures

Diagnostic Procedures

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  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step.
  2. Turn ignition off. Remove fuel cap. Turn ignition on. Using scan tool, observe fuel tank pressure. If fuel tank pressure is -1 to 1 in. H2O, go to next step. If fuel tank pressure is not -1 to 1 in. H2O, diagnose fuel tank pressure sensor. See SYSTEM/COMPONENT TESTS - 5.7L article.
  3. Install fuel filler cap. Install EVAP Pressure/Purge Diagnostic Station (J 41413) to EVAP service port. Ensure gauges on test equipment is zeroed before starting test. Using scan tool, command EVAP vent valve closed. Attempt to pressurize EVAP system to 5 in. H2O using diagnostic station. Monitor pressure using gauge on diagnostic station. If scan tool indicates that fuel tank pressure is -1 to 1 in. H2O, go to next step. If scan tool does not indicate that fuel tank pressure is -1 to 1 in. Hg, diagnose EVAP control system. See SYSTEM/COMPONENT TESTS - 5.7L article.
  4. Maintain EVAP pressure at 5 in. H2O. Using scan tool, command EVAP vent valve off (open). If EVAP pressure returns to -1 to 1 in. H2O within 10 seconds, see DIAGNOSTIC AIDS. If EVAP pressure does not return to -1 to 1 in. H2O within 10 seconds, go to next step.
  5. Turn rotary switch on diagnostic station to RELEASE PRESSURE position. Disconnect vent hose from EVAP canister. Disconnect fuel tank vapor line and EVAP purge line from EVAP canister. Block fuel tank vapor line fitting at EVAP canister. Connect a hand-held vacuum pump to EVAP purge line fitting on EVAP canister. Apply 5 in. Hg. If 5 in. Hg can be obtained and held, go to step 11). If vacuum cannot be obtained or held, go to next step.
  6. Check for kinked, pinched or blocked vent hose between EVAP canister and vent valve. Repair as necessary. After repairs, go to step 13). If vent hose is okay, go to next step.
  7. Turn ignition off. Disconnect vent valve connector. Turn ignition on, engine off. Connect a test light between battery voltage and vent valve connector terminal "A". If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
  8. Turn ignition off. Disconnect VCM harness connector. Connect test light between battery voltage and EVAP vent valve connector terminal "A". If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
  9. Repair short to ground in EVAP vent control circuit. After repairs, go to step 13).
  10. Replace EVAP vent valve. After replacing valve, go to step 13).
  11. Check EVAP vapor 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 valve on (closed). Using diagnostic station, pressurize EVAP system to 5 in. H2O. Using scan tool, command EVAP vent valve off (open). Observe gauge on diagnostic station. If EVAP pressure returns to 0 in. H2O within 10 seconds, go to next step. If EVAP pressure does not return to 0 in. H2O, repeat step 2).
  14. Using scan tool, select DTC, CLEAR INFO function. Perform SERVICE BAY TEST for EVAP system. After performing test, go to next step.
  15. Using scan tool, select Read and Record INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs. If no DTCs are displayed, system is okay.
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