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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 89 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.0L)DIAGNOSTIC TESTSDTC P1404: EGR SYSTEM 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 is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: If DTC P0403 is set, diagnose DTC before continuing with this test. See DTC P0403: EGR SOLENOID CONTROL CIRCUIT .
  2. Install a scan tool. Start the engine. With a scan tool, observe the EGR position sensor parameter. Does the scan tool indicate that the EGR position sensor is at 0 percent? If yes, go to next step. If no, go to step  5.
  3. Using scan tool, command EGR valve from zero percent to 100 percent. If desired EGR position remains close to EGR position sensor at all commanded positions, go to next step. If desired EGR position does not remain close to EGR position sensor at all commanded positions, go to step  6.
  4. Using scan tool, observe and record 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 recorded 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 the ignition OFF. Disconnect EGR valve connector. Turn ignition on. 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 EGR position sensor to the low reference circuit of EGR position sensor. Does the Digital Multimeter (DMM) display voltage about 5 volts? If yes, go to next step. If no, go to step  8.
    7. NOTE: If fuse blows, locate and repair a short to ground in the signal circuit.
  7. Connect a fused jumper between the 5-volt reference circuit of the EGR position sensor and EGR valve position signal circuit of EGR position sensor. Does scan tool indicate that the EGR position sensor value is about 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 DMM display voltage about 5 volts? If yes, go to step  10. If no, go to step  12.
  9. Test the EGR valve 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 low reference 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. Check for poor connections at EGR valve connector. Did you find and correct the condition? If yes, go to step  17. If no, go to step  16.
  14. Check for poor connections at PCM connectors. Did you find and correct the condition? If yes, go to step  17. If no, go to step  16.
  15. Replace EGR valve. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  17.
  16. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  17. Use the scan tool in order to clear the DTCs. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  18. With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, 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.