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 numbers below refer to the step numbers on the diagnostic table.

3: 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.
5: Determine if the HVAC Control Module, Body Control Module, or Powertrain Control Module have set DTC's which may affect HVAC operation are present.
6: 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.
7: Answer Yes if the first three characters of the DTC name begins with B10; regardless of the last two characters.

Diagnostic System Check - HVAC Systems - Automatic

Step	Action	Yes	No
1	Did you review A Diagnostic Starting Point - Heating, Ventilation and Air Conditioning?	Go to Step 2	Go to Diagnostic Starting Point - Heating, Ventilation and Air Conditioning in Heating, Ventilation and Air Conditioning
2	Install a scan tool. Does the scan tool power up?	Go to Step 3	Go to Scan Tool Does Not Power Up in Data Link Communications
3	Turn ON the ignition, with the engine OFF. Attempt to establish communication with the following control modules: HVAC Control Module Body Control Module Powertrain Control Module Does the scan tool communicate with the control modules?	Go to Step 4	Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
4	IMPORTANT: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool. Rotate the ignition switch through all positions while observing the Ignition Switch Power Mode parameter. Does the Ignition Switch parameter reading match the ignition switch position for all switch positions?	Go to Step 5	Go toPower Mode Mismatch in Body Control System
5	Select the display DTCs function on the scan tool for the following modules: HVAC Control Module Body Control Module Powertrain Control Module Does the scan tool display any DTCs?	Go to Step 6	Go to Symptoms - HVAC Systems - Automatic
6	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 7
7	Does the scan tool display DTC B10XX?	Go to Diagnostic Trouble Code (DTC) List in Body Control Systems	Go to Step 8
8	Does the scan tool display any DTCs that are associated with the charging system?	Go to Diagnostic Trouble Code (DTC) List in Engine Electrical	Go to Step 9
9	Does the scan tool display any DTCs that are associated with the HVAC system?	Go to Diagnostic Trouble Code (DTC) List	Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 4.8L, 5.3L, and 6.0L, Diagnostic Trouble Code (DTC) List in Engine Controls - 8.1L, Diagnostic Trouble Code (DTC) List in Engine Controls - 4.3L, Diagnostic Trouble Code (DTC) List in Engine Controls - 6.6L (LB7), or Diagnostic Trouble Code (DTC) List in Engine Controls - 6.6L (LLY)