Test Description

The numbers below refer to the step numbers on the diagnostic table. See Fig 1.

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.
Fig 1: Diagnostic System Check Diagnostic Table - Lighting Systems
Courtesy of GENERAL MOTORS CORP.