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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 341 (STARTING SYSTEM)DIAGNOSTIC INFORMATIONDIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICAL
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic System Check - Engine Electrical

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic System Check - Engine Electrical
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform the Battery Inspection/Test. See BATTERY TESTING & INSPECTION in GENERATORS & REGULATOR article under ELECTRICAL. Does the battery pass the test? If so, go to next step.
  2. Install a scan tool. Turn ON the ignition, with the engine OFF. Does the scan tool power up? If so, go to next step. If not, go to SCAN TOOL DOES NOT POWER UP in BODY CONTROL MODULES article, under ACCESSORIES & EQUIPMENT.
    NOTE: Lack of communication may be because of a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
  3. Attempt to communicate with each of the following modules on the class 2 serial data circuit:
    • Body Control Module (BCM)
    • Powertrain Control Module (PCM)
    • Instrument Panel Cluster (IPC)
    Does the scan tool communicate with all modules on the class 2 serial data circuit? If so, go to next step. If not, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in BODY CONTROL MODULES article under ACCESSORIES & EQUIPMENT.
    NOTE: The symptom list in Symptoms will determine the correct diagnostic procedure to use.
  4. Select the BCM, IPC and the PCM display DTC function on the scan tool. Does the scan tool display any DTCs? If so, go to next step. If not, go to SYMPTOMS - ENGINE ELECTRICAL .
    NOTE: The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will collect all the available information before you perform tests.
  5. Does the scan tool display any DTCs which begin with a U? If so, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in BODY CONTROL MODULES article, under ACCESSORIES & EQUIPMENT. If not, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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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.