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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 530 (BATTERY, CHARGING SYSTEM AND STARTING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDIAGNOSTIC SYSTEM CHECK - ENGINE ELECTRICALTEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic

Test Description

1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Description
WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 4:  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.
  2. 5:  The symptom list in Symptoms will determine the correct diagnostic procedure to use.
  3. 6:  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.
Diagnostic System Check - Engine Electrical

Step Action Yes No
1 Perform the Battery Inspection/Test. Refer to Battery Inspection/Test .
Does the battery pass the test?		 Go to Step 2  -
2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
Does the scan tool power up?		 Go to Step 3  Go to Scan Tool Does Not Power Up in Data Link Communications
3
IMPORTANT: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
  1. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
  2. Rotate the ignition switch through all positions while observing the Class 2 Power Mode parameter.
Does the ignition switch parameter reading match the ignition switch position for all switch positions?		 Go to Step 4  Go to Power Mode Mismatch in Body Control System
4 
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to communicate with each of the following modules on the class 2 serial data circuit:
    • Body Control Module (BCM)
    • Instrument Panel Cluster (IPC)
    • Powertrain Control Module (PCM)
Does the scan tool communicate with any module on the class 2 serial data circuit?		 Go to Step 5  Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
5 
  1. Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set.
  2. Record all of the displayed DTCs, the DTC status, and the module which set the DTC.
Does the scan tool display any DTCs?		 Go to Step 6  Go to Symptoms - Engine Electrical 
6  Does the scan tool display any DTCs which begin with a "U"? Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications Go to Step 7 
7 Does the scan tool display DTC B1000? Go to Diagnostic Trouble Code (DTC) List in Body Control System Go to Diagnostic Trouble Code (DTC) List 
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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.