Test Description

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. 4. The symptom table will determine the correct diagnostic procedure to use.
3. 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.

   Fig 1: Diagnostic System Check - Defogger

   Courtesy of GENERAL MOTORS CORP.