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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 4.3 W, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0352-P0452DTC P0404DTC P0404: EGR VALVE OPEN PINTLE POSITION (4.3L "L", "M", "S" & "T" SERIES)DIAGNOSTIC PROCEDURES
1999 GMC Forward Control 4.3 W, Standard

Diagnostic Procedures

1999 GMC Forward Control 4.3 W, StandardSECTION 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. Turn ignition on, with engine off. Using scan tool, command EGR valve to 20, 50, 70, 100 percent. If actual EGR position follow the desired/commanded EGR position, go to step  5. If actual EGR position does not follow the desired/commanded EGR position, go to next step.
  3. Turn ignition off. Disconnect EGR harness connector. Turn ignition on, engine off. Using a test light connected to battery voltage, probe EGR valve sensor ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step  7.
  4. Connect test light to ground. Probe EGR feed control circuit at EGR harness connector. Using scan tool, command EGR valve to 20, 50, 70, 100 percent. If test light glows brighter, flash or maintain a steady dim glow as EGR is commanded, go to step  6. If test light does not glow as EGR is commanded, go to step  10.
  5. DTC is intermittent. Check for additional DTCs set. If DTCs are set, diagnose affected DTCs. If no additional DTCs are set, see DIAGNOSTIC AIDS .
  6. Turn ignition on. Connect test light between battery voltage and EGR valve ground circuit. If test light illuminates, go to step  9. If test light does not illuminate, go to step  8.
  7. Check for open or poor connection in EGR valve feed control circuit. Repair as necessary. After repairs, go to step  22. If circuit or connection is okay, go to step  20.
  8. Check for open or poor connection in EGR valve feed control circuit. Repair as necessary. After repairs, go to step  22. If circuit or connection is okay, go to step  20.
  9. Connect test light between ground and EGR pintle position signal circuit. If test light illuminates, go to step  11. If test light does not illuminate, go to step  12.
  10. Using test light connected to ground, probe EGR valve feed control circuit without commanding EGR valve with scan tool. If test light illuminates, go to step  13. If test light does not illuminate, go to step  14.
  11. Check signal circuit for short to voltage. Repair as necessary. After repairs, go to step  22. If circuit is okay, go to step  20.
  12. Using DVOM, check voltage in 5-volt reference circuit. If voltage reading is about 5 volts, go to step  15. If voltage reading is not about 5 volts, go to step  16.
  13. Check EGR valve feed control circuit for short to voltage. Repair as necessary. After repairs, go to step  22. If circuit is okay, go to step  20.
  14. Connect test light between battery voltage and EGR valve feed control circuit. If test light illuminates, go to step  17. If test light does not illuminate, go to step  18.
  15. Check EGR sensor ground circuit for poor connection at EGR valve. Repair as necessary. After repairs, go to step  22. If connection is okay, go to step  19.
  16. Check 5-volt reference circuit for short to voltage. Repair as necessary. After repairs, go to step  22. If circuit is okay, go to step  20.
  17. Check EGR valve feed control circuit for short to ground. Repair as necessary. After repairs, go to step  22. If circuit is okay, go to step  20.
  18. Check EGR valve feed control circuit for open or poor connection at EGR valve harness connector. Repair as necessary. After repairs, go to step  22. If circuit is okay, go to step  20.
  19. Replace EGR valve. After replacing EGR valve, go to step  22.
  20. Check VCM harness connector for poor connection. Repair as necessary. After repairs, go to step  22. If connection is okay, go to next step.
  21. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
  22. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool did not indicate that this test ran and passed, repeat step  2.
  23. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no additional DTCs are set, system is okay.
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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.