1999 GMC Forward Control 5.7 R, AutomaticFACTORY OEM SERVICE PROCEDURE

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. Ensure engine coolant level is full. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to battery voltage, probe ENGINE HOT light circuit at PCM harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  6.
  3. Turn ignition off. Reconnect PCM harness connector. Check temperature gauge using scan tool. If gauge is indicating excessive temperature, check and repair temperature gauge circuit. If gauge does not indicate excessive temperature, go to next step.
  4. Turn ignition on, with engine off. Using DVOM, check voltage to ENGINE HOT light circuit at PCM harness connector. If voltage reading is near battery voltage, go to step  6. If voltage reading is not near battery voltage, go to next step.
  5. Check ENGINE HOT light circuit for short to ground. Repair as necessary. After repairs, go to step  8. If circuit is okay, go to step  7.
  6. Check for open in ignition feed circuit to ENGINE HOT light indicator. Check for poor terminal connection at PCM. Repair as necessary. After repairs, go to step  9. If no problems were found, go to next step.
  7. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step  9.
  8. Locate and repair short to ground at ENGINE HOT light circuit. After repairs, go to next step.
  9. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step  2. If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.
Factory Service Tools

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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.

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