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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 P0650: MALFUNCTION INDICATOR LIGHT CONTROL CIRCUITDIAGNOSTIC 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  under SELF-DIAGNOSTIC SYSTEM. After performing Diagnostic System Check - Engine Controls, go to next step.
    2. NOTE: If MIL fuse is open, locate and repair a short to ground in MIL battery voltage circuit or a shorted cluster.
  2. Inspect the fuse that supplies voltage to the MIL. Was the fuse open? If yes, go to step  12. If no, go to next step.
    3. NOTE: If jumper fuse opens, locate and repair short to voltage in MIL control circuit or a shorted cluster.
  3. Turn ignition off. Disconnect PCM. Install a 3-amp fused jumper between the MIL control circuit at the PCM harness connector and a good ground. Turn on the ignition, with the engine off. Is the MIL illuminated? If yes, go to next step. If no, go to step  5.
  4. Leaving ignition on, remove jumper. Is MIL illuminated? If yes, go to step  7. If no, go to step  9.
  5. Remove instrument cluster. Test the MIL control circuit for an open and repair as necessary. Did you find and correct the condition? If yes, go to step  12. If no, go to next step.
  6. Test the MIL battery voltage circuit for an open and repair as necessary. Did you find and correct the condition? If yes, go to step  12. If no, go to step  8.
  7. Remove instrument cluster. Test the MIL control circuit for a short to ground and repair as necessary. Did you find and repair the condition? If yes, go to step  12. If no, go to step  10.
  8. Inspect the cluster harness connector for faulty connections and repair as necessary. Did you find and repair the condition? If yes, go to step  12. If no, go to step  10.
  9. Inspect the PCM and the PCM harness connector for faulty connections and repair as necessary. Did you find and correct the connection? If yes, go to step  12. If no, go to step  11.
  10. Repair or replace instrument cluster. After repairs, go to step  12.
  11. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  12. 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.
  13. 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.