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HOMESERVICE MANUALSCHEVROLET1999CHEVY EXPRESS G1500, VAN CARGO, 5.7 RREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0352-P0452DTC P0446DTC P0446: EVAP SYSTEM CANISTER VENT BLOCKED (3.5L "W" BODY)DIAGNOSTIC PROCEDURES
1999 Chevrolet Chevy Express G1500, Van Cargo, 5.7 R

Diagnostic Procedures

1999 Chevrolet Chevy Express G1500, Van Cargo, 5.7 RSECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
  2. If DTC P0449 is also set, diagnose DTC P0449 before proceeding. If DTC P0449 is not set, check EVAP system for improperly routed, kinked or damaged EVAP purge and tank vent lines. Repair as necessary. After repairs, go to step  15. If no problems were found, go to next step.
  3. Turn ignition off. Remove fuel filler cap. Wait 30 seconds, then replace filler cap. Turn ignition on, with engine off. Using scan tool, monitor EVAP fuel tank pressure sensor display. If scan tool displays -10 in. H2O or less, go to next step. If scan tool does not display -10 in. H2O or less, go to step  10.
  4. Start and operate engine at idle. Using scan tool, select EVAP PURGE/SEAL function. Command enough EVAP purge to obtain -10 in. H2O, then seal the system. While monitoring EVAP fuel tank pressure sensor display, command EVAP vent valve OPEN (press Exit). If pressure sensor reading drops to near zero when zero percent EVAP purge is commanded and vent valve opened, fault is not present. If pressure reading does not drop to near zero when zero percent EVAP purge is commanded and vent valve opened, go to next step.
  5. Turn ignition off. Disconnect fuel tank vapor and EVAP purge lines from EVAP vapor canister. Plug canister fitting for fuel tank vapor line. Connect a hand-held vacuum pump to EVAP purge line canister fitting. Turn ignition on, with engine off. Using scan tool, command EVAP vent valve ON (closed). Using vacuum pump, apply and hold 5 in. Hg. Command EVAP vent valve OFF (open). If vacuum drops when vent valve is opened, go to step  8. If vacuum does not drop when vent is opened, go to next step.
  6. Leave system connected as in previous step. Disconnect and plug vent line at EVAP vent valve. Using vacuum pump, apply 5 in. Hg. Monitor vacuum pump gauge as plug from vent line is removed. If vacuum drops, go to step  11. If vacuum does not drop, go to next step.
  7. Check EVAP vent line from EVAP vent valve for restrictions. Replace as necessary. After repairs, go to step  10. If no problem is found, go to step  12.
  8. Check fuel tank vapor line for restriction. Replace as necessary. After replacing vapor line, go to step  15. If vapor line is okay, go to next step.
  9. Turn ignition off. Remove plug and vacuum pump. Reconnect EVAP vapor canister purge and vent lines. Connect EVAP pressure/purge diagnostic station to EVAP system service port. Operate engine. Using scan tool, select Purge/Seal function to command EVAP vent solenoid ON to varying vacuum levels with engine running and quickly seal the system using scan tool. Compare EVAP pressure/purge diagnostic station's vacuum gauge and scan tool's reading. If both readings are within plus or minus 2 in. Hg of each other, go to step  2. If both readings are not within plus or minus 2 in. Hg of each other, go to step  13.
  10. Turn ignition off. Disconnect EVAP fuel tank pressure sensor harness connector. Disconnect PCM harness connector C1. Using a DVOM, check resistance of sensor ground circuit between PCM harness connector and EVAP fuel tank pressure sensor harness connector. If resistance is 5 ohms or less, go to step  13. If resistance is not 5 ohms or less, go to step  14.
  11. Replace EVAP vent valve. After replacing vent valve, go to step  15.
  12. Replace EVAP vapor canister. After replacing vapor canister, go to step  15.
  13. Replace EVAP fuel tank pressure sensor. After replacing sensor, go to step  15.
  14. Repair open in EVAP fuel tank pressure sensor ground circuit. After repairs, go to next step.
  15. Using scan tool, select DTC and CLEAR DTC INFO functions. Clear DTCs. Operate vehicle within conditions required to set DTC. If scan tool displays that this test ran and passed, go to next step. If scan tool does not display that this test ran and passed, go to step  2.
  16. Using scan tool, select CAPTURED INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.