Diagnostic Aids

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 condition may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Inspect the air delivery system for the following conditions:
- A dirty HVAC air filter, if applicable
- An obstruction to the airflow
- Air leaks
- Misaligned air ducts
- Broken or binding linkages or doors

Air Delivery Improper

Step	Action	Value(s)	Yes	No
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views
1	Did you perform the HVAC Diagnostic System Check?	-	Go to Step 2	Go to Diagnostic System Check - HVAC Systems - Manual
2	Turn ON the ignition, with the engine OFF. Place the blower motor switch in the OFF position. Is the blower motor OFF?	-	Go to Step 3	Go to Blower Motor Always On
3	Place the blower motor switch in each speed position. Does the blower motor operate in any of the speed positions?	-	Go to Step 4	Go to Blower Motor Inoperative
4	Does the blower motor operate in each speed position?	-	Go to Step 5	Go to Blower Motor Malfunction
5	With a scan tool, observe the Mode Select Position parameter in the Heating and Air Conditioning data list. Place the mode switch in each position. Does the scan tool indicate that the Mode Select Position parameter displays the correct mode switch positions?	-	Go to Step 6	Go to Step 7
6	Place the blower motor switch in the maximum speed position. Place the mode switch in the bi-level position. Place the recirculation switch in the ON position. Observe the drive shaft of the recirculation actuator. Place the recirculation switch in the OFF position. Does the recirculation door move from the recirculation position to the outside air position?	-	Go to Diagnostic Aids	Go to Air Recirculation Malfunction
7	Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition?	-	Go to Step 9	Go to Step 8
8	Replace the HVAC control module. Refer to HVAC Control Module Replacement . Did you complete the replacement?	-	Go to Step 9	-
9	Operate the system in order to verify the repair. Did you correct the condition?	-	System OK	Go to Step 2