GM Service Manual Online
For 1990-2009 cars only

All the HVAC control module diagnostic trouble codes (DTC) are displayed with a blink code on the A/C, recirculation and rear defrost LED's. The DTC will flash after diagnostic mode is entered. If there is no DTC present all of the LED's will flash quickly. If a DTC is present, the rate at which the LED will flash will be slower than the quick flash associated with no DTC. The LED will flash 8 times then repeat this until the code is cleared or ignition is turned OFF. To enter diagnostic mode perform the following procedure:

  1. Turn Off the ignition.
  2. Press and hold the following HVAC control module switches:
  3. • A/C request switch
    • Recirculation switch
    • Rear defrost switch
  4. While pressing the switches, turn the ignition to the Run position.
  5. Wait 5 seconds.
  6. Observe the switch LED's.
  7. The LED's will flash quickly if there is no DTC's are present.
  8. If 1 of the LED's flash 8 times then there is an HVAC control module DTC. Refer to the following table to determine DTC:

DTC

Flashing Switch LED

Code Description

001

Rear Defrost Switch

Mode Actuator Failure

010

Recirculation Switch

HVAC Control Module Failure

100

A/C Request Switch

Air Temperature Actuator Failure

There is only one DTC for each of the HVAC control module switch LED's. If there is only 1 DTC that LED will flash 8 times slowly while the other LED will flash quickly to indicate no DTC. If multiple DTC are set they will flash 8 times slowly.

Refer to Symptoms - HVAC Systems - Manual if a DTC is present. To exit diagnostic mode turn the ignition to the OFF position.