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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 238 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.3L)DIAGNOSTIC TESTSDTC P0650: MIL 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 6 other vehicles, including the 2003 GMC Sonoma, 2003 GMC Safari, 2003 GMC Jimmy, 2003 Chevrolet S10 Pickup, and 2003 Chevrolet Blazer. 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, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Verify whether the Instrument Panel (IP) is operational. If the IP is completely inoperative, see appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Verify whether the MIL turns ON and OFF when commanded. Turn ignition on, with engine off. Command the MIL ON and OFF using the scan tool. Repeat the commands as necessary. Does the MIL turn ON and OFF when commanded? If yes, go to next step. If no, go to step  4.
  3. Observe the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observe. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  4. Inspect the fuse that supplies battery voltage to the MIL. Is the fuse open? If yes, go to step  10. If no, go to next step.
  5. Turn ignition off. Disconnect the PCM. Turn ON the ignition. Is the MIL OFF? If yes, go to next step. If no, go to step  11.
  6. Turn ignition off. Remove the fuse that supplies voltage to the MIL. Turn ignition on, with engine off. Connect a Digital Volt-Ohmmeter (DVOM) from the MIL control circuit to a good ground. Is the voltage zero volts? If yes, go to next step. If no, go to step  12.
  7. Turn ignition off. Reinstall the fuse that supplies voltage to the MIL. Turn ignition on, with engine off. Probe the MIL control circuit in the PCM harness connector with a fused jumper wire connected to ground. Is the MIL ON? If yes, go to step  15. If no, go to next step.
  8. Turn ignition off. Remove the IP. Probe the MIL battery voltage circuit at the IP harness connector with a test light connected to a good ground. Is the test light illuminated? If yes, go to next step. If no, go to step  13.
  9. Test the MIL control circuit for an open or high resistance and repair as necessary. Did you find and correct a condition? If yes, go to step  18. If no, go to step  14.
  10. Repair short to ground in the battery positive voltage circuit. After repairs, go to step  18.
  11. Repair short to ground in the MIL control circuit. After repairs, go to step  18.
  12. Repair short to voltage in the MIL control circuit. After repairs, go to step  18.
  13. Repair open in the MIL battery positive voltage. After repairs, go to step  18.
  14. Inspect for poor connections at the IP and repair as necessary. Did you find and correct the condition? If yes, go to step  18. If no, go to step  16.
  15. Inspect for poor connections at the PCM and repair as necessary. Did you find and correct the condition? If yes, go to step  18. If no, go to step  17.
  16. Replace IPC. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After repairs, go to step  18.
  17. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  18. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  19. Observe the stored information, Capture Info with a scan tool. 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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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.