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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 720 (CRUISE CONTROL SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDIAGNOSTIC SYSTEM CHECK - CRUISE CONTROLTEST 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 Chevrolet Corvette. 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. 2:  Lack of communication may be due to a malfunction in the class 2 serial data circuit. The specified procedure will determine the particular condition.
  2. 5:  The presence of DTCs which begin with "U" indicates that some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
Diagnostic System Check - Cruise Control

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 the ignition ON, with the engine OFF.
  2. Attempt to establish communication with the following modules:
    • The powertrain control module (PCM)
    • The electronic brake control module (EBCM)
Does the scan tool communicate with the modules listed above?		 Go to Step 3  Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
3
IMPORTANT: The engine may start during the following step. Turn the engine OFF as soon as you have observed the Crank power mode.
  1. With a scan tool, access the Class 2 Power Mode in the Diagnostic Circuit Check.
  2. Rotate the ignition switch through all positions while observing the System Power Mode parameter.
Does the System Power Mode 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 Select the DTCs function on the scan tool for the following modules:
  • The powertrain control module (PCM)
  • The electronic brake control module (EBCM)

Does the scan tool display any DTCs?		 Go to Step 5  Go to Symptoms - Cruise Control 
5  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 6 
6 Does the scan tool display DTC P0562, P0563, P0615, or P01638? Go to Diagnostic Trouble Code (DTC) List in Engine Electrical 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.