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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 335 (CHARGING SYSTEM)ON-VEHICLE TESTINGENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECKDIAGNOSTIC PROCEDURE
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedure

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedure
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2003 GMC Sonoma, 2003 GMC Jimmy, 2003 Chevrolet S10 Pickup, 2003 Chevrolet Blazer, and 2002 GMC Sonoma. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform battery test and inspection. See BATTERY TESTING & INSPECTION under ON-VEHICLE TESTING. If battery passed test, go to next step. If battery did not pass test, replace battery.
  2. Connect scan tool to Data Link Connector (DLC). DLC is located below left side of instrument panel. Turn ignition switch to RUN position. If scan tool powers up, go to next step. If scan tool does not power up, perform appropriate test in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
    3. NOTE: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
  3. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool. Rotate the ignition switch through all positions while observing the Class 2 Power Mode parameter. The ignition switch parameter reading should match the ignition switch position for all switch positions. If reading is as specified, go to next step. If reading is not as specified, see appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
  4. Turn ignition switch to RUN position. Using scan tool, attempt to communicate with Body Control Module (BCM), Driver's Information Center (DIC), Instrument Panel Cluster (IPC) and Powertrain Control Module (PCM). If scan tool communicates with BCM, DIC, IPC and PCM, go to next step. If scan tool does not communicate with BCM, DIC, IPC and PCM, perform appropriate test in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
  5. Using scan tool, select DISPLAY DTC's function for each module. Record all DTC's displayed, DTC status and specific module which set DTC. If scan tool displays any DTC's, go to next step. If scan tool does not display DTC's, repair starting system by symptom. See SYMPTOM INDEX  table under SYSTEM TESTS.
  6. If scan tool displays DTC's which begin with "U", perform appropriate test in accordance with DTC retrieved. See appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If scan tool does not display DTC's which begin with "U", go to next step.
  7. If scan tool displays DTC's which begin with "B", perform appropriate test in accordance with DTC retrieved. See appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If scan tool does not display DTC's which begin with "B", perform appropriate test in accordance with DTC retrieved. See 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.