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. Using scan tool, check for PCM DTCs. If any PCM related DTCs are stored, diagnose affected DTCs. If no PCM related DTCs are set, go to next step.
  3. Check for ABS related DTCs. If any ABS related DTCs are stored, diagnose affected DTCs. If no ABS related DTCs are set, go to next step.
  4. Check for poor or intermittent connection at PCM and ABS components. Check for short or open in Class II serial data circuit from PCM to ABS system. Repair as necessary. After repairs, go to step 6. If connections or circuits are okay, go to next step.
  5. Perform ABS diagnostic system check. See appropriate ANTI-LOCK article in BRAKES. Repair as necessary. After repairs, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. If repairs were not necessary, go to next step.
  6. Read and record FAILURE RECORDS data for this DTC. Clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step  1. 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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