Test Description

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 Chevrolet Tahoe, 2002 Chevrolet Suburban, and 2002 Chevrolet Avalanche. 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 Rear Seat Audio (RAS) Control Module, HVAC Control Module, Body Control Module or Powertrain Control Module have set DTCs which may affect HVAC operation are present.
6: The presence of DTCs which begin with "U", except U1500, indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed. Be sure to diagnose all other "U" codes before diagnosing a U1500.
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
2	Install a scan tool. Does the scan tool power up?	Go to Step 3	Go to SCAN TOOL DOES NOT POWER UP
3	Turn ON the ignition, with the engine OFF. Attempt to establish communication with the following control modules: Rear Seat Audio (RSA) Control Module 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 D
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 to POWER MODE MISMATCH
5	Select the display DTCs function on the scan tool for the following modules: Rear Seat Audio (RSA) Control Module 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", except U1500?	Go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE	Go to Step 7
7	Does the scan tool display DTC B10XX?	Go to BODY CONTROL SYSTEMS DIAGNOSTIC TROUBLE CODE (DTC) LIST	Go to Step 8
8	Does the scan tool display any DTCs which begin with a P that are associated with the charging system?	Go to ENGINE ELECTRICAL DIAGNOSTIC TROUBLE CODE (DTC) LIST	Go to Step 9
9	Does the scan tool display U1500 or any DTCs which begin with a P or B that are associated with the HVAC system?	Go to Diagnostic Trouble Code (DTC) List	Go to DIAGNOSTIC TROUBLE CODE DEFINITIONS (4.8L, 5.3L, & 6.0L ENGINE) or DIAGNOSTIC TROUBLE CODE DEFINITIONS (8.1L ENGINE)