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Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. 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 or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
  2. 3:  This step determines if an ignition switch power mode condition exists. The specified procedure will determine which diagnostic path is to be followed.
  3. 4:  This step determines if a Body Control Module (BCM) DTC based diagnostic path or a symptom based diagnostic path are to be followed.
  4. 5:  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.
  5. 6:  This step displays stored system related DTCs to be diagnosed.
Diagnostic System Check - Lighting Systems

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.
Does the scan tool communicate with the body control module?		 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 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 on the Scan Tool. Refer to the Serial Data Power Mode table within Body Control System Description and Operation in Body Control System for a list of the power mode states that correspond to each ignition switch position.
Does the ignition switch parameter reading match the ignition switch position for OFF, RUN, and CRANK?		 Go to Step 4  Go toPower Mode Mismatch in Body Control System
4  Select the BCM display DTCs function on the scan tool.
Does the scan tool display any DTCs?		 Go to Step 5  Go to Symptoms - Lighting Systems 
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 B1000, B1004, B1007, B1009, B1397, B1420, or B1440? Go to Diagnostic Trouble Code (DTC) List in Body Control System Go to Diagnostic Trouble Code (DTC) List 
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