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Test Description

The numbers below refer to the step numbers on the diagnosis table.

  1. 3. Lack of communication may be due to a partial malfunction of the class 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. 4. Determine if the Powertrain Control Module has set DTCs which may affect HVAC operation are present.
  3. 5. The presence of DTCs which begin the "U" indicate some other module is not communicating. The speed procedure will compile all the available information before tests are performed.
    Fig 1: Diagnostic System Check - HVAC Systems - Manual
    G01645766Courtesy of GENERAL MOTORS CORP.
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