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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 844 (MIRROR SYSTEM & WINDOW SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDIAGNOSTIC SYSTEM CHECK - DEFOGGERTEST 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 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The number(s) below refer to the step number(s) on the diagnostic table.

  1. 2:  Lack of communication may be due to a partial malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
  2. 3:  The symptom table will determine the correct diagnostic procedure to use.
  3. 4:  The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
Diagnostic System Check - Defogger

Step Action Yes No
1 Install a scan tool.
Does the scan tool power up?		 Go to Step 2  Go to Scan Tool Does Not Power Up in Data Link Communications
2 
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to establish communication with the body control module (BCM).
Does the scan tool communicate with the module?		 Go to Step 3  Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
3  Select the display DTCs function on the scan tool for the body control module (BCM).
Does the scan tool display any DTCs?		 Go to Step 4  Go to Symptoms - Stationary Windows 
4  Does the scan tool display DTCs that begin with "U"? Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications Go to Step 5 
5 Does the scan tool display DTC B1000, B1001, B1372, or B1382? Go to Diagnostic Trouble Code (DTC) List in Body Control System Go to Step 6 
6 Does the scan tool display DTC B1327 or B1328? Go to Diagnostic Trouble Code (DTC) List in Engine Electrical Go to Diagnostic Trouble Code (DTC) List 
RENDER: 1.0x

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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.