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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 78 (ENGINE CONTROL SYSTEM SELF-DIAGNOSTICS - 3.8L)DIAGNOSTIC TESTSDTC P1404: EGR CLOSED POSITION PERFORMANCEDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 Pontiac Grand Prix, 2002 Pontiac Bonneville, 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, and 2002 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS . After performing Diagnostic System Check - Engine Controls, go to next step.
    2. NOTE: If DTC P0403 is set, diagnose DTC P0403 first. See DTC P0403: EGR SOLENOID CONTROL CIRCUIT .
  2. Install scan tool. Start engine. Using scan tool, observe EGR position sensor parameter. Does the scan tool indicate that the EGR position sensor is at zero percent? If yes, go to next step. If no, go to step  5.
  3. Turn ignition on, engine off. Using scan tool, command EGR valve from zero percent to 100 percent. Does the desired EGR position remain within 15 percent of the EGR position sensor at all commanded positions? If yes, go to next step. If no, go to step  6.
  4. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within conditions for running DTC or as close to FREEZE FRAME/FAILURE RECORDS data as possible. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. Turn ignition off. Disconnect EGR valve. Turn ignition on, engine off. Using scan tool, observe EGR position sensor parameter. Does the scan tool indicate that the EGR position sensor is at zero percent? If yes, go to next step. If no, go to step  9.
  6. Measure the voltage from the 5-volt reference circuit of the EGR position sensor to the ground circuit of the EGR position sensor. Does the DMM display voltage near 5.0 volts? If yes, go to next step. If no, go to step  8.
    7. NOTE: If fuse blows, locate and repair short to ground in signal circuit.
  7. Connect a fused jumper between the 5-volt reference circuit of the EGR position sensor and the EGR pintle position signal circuit of the EGR position sensor. Does the scan tool indicate that the EGR position sensor is near 100 percent? If yes, go to step  13. If no, go to step  11.
  8. Measure the voltage from the 5-volt reference circuit of the EGR position sensor to a good ground. Does the DMM display voltage near 5 volts? If yes, go to step  10. If no, go to step  12.
  9. Test the EGR pintle position signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  17. If no, go to step  14.
  10. Test the EGR position sensor ground circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step  17. If no, go to step  14.
  11. Test the signal circuit for high resistance or a high resistance short to ground. Did you find and correct the condition? If yes, go to step  17. If no, go to step  15.
  12. Test the 5-volt reference circuit of the EGR position sensor for an open, a short to ground, or a short to voltage. Did you find and correct the condition? If yes, go to step  17. If no, go to step  15.
  13. Inspect for poor connections at the harness connector of the EGR valve. Did you find and correct the condition? If yes, go to step  17. If no, go to step  15.
  14. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step  17. If no, go to step  16.
  15. Replace EGR valve. After repairs, go to step  17.
  16. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  17. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within Conditions for Running DTC. Does DTC run and pass? If yes, go to next step. If no, go to step  2.
  18. Using scan tool, observe stored information. Does scan tool displays any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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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.