GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

If vehicle is equipped with K08 Coolant Heater also known as Fuel Operated Heater and Auxiliary Heater option, be sure to check for trouble codes in the scan tool under Powertrain, Auxiliary Heater Control Module.

Test Description

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

  1. This checks for proper cooling system operation.

  2. The voltage will vary between 0-12 volts during normal operation. The HVAC control assembly connector must be connected during this step.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: Temperature cannot be adjusted or the heating is insufficient.

1

Did you review the HVAC operation and perform the necessary inspections?

--

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2

  1. Turn ON the ignition, with the engine OFF.
  2. Place the mode switch in any position except OFF.
  3. Place the blower motor switch in each speed position.

Does the blower motor operate in any of the speed positions?

--

Go to Step 3

Go to Blower Motor Inoperative

3

Does the blower motor operate correctly for each speed position?

--

Go to Step 4

Go to Blower Motor Malfunction

4

  1. Ensure the blower motor switch is ON.
  2. Select an air outlet mode.

Does air flow out of the selected HVAC outlet ducts?

--

Go to Step 5

Go to Air Delivery Improper

5

Inspect the cooling system for the following:

    • A low coolant level
    • A loose or worn accessory drive belt
    • A leaking radiator hose or heater hoses
    • A kinked radiator hose or heater hoses
    • A missing radiator cap pressure seal
    • A leaking radiator cap

Did you find and correct the condition?

--

Go to Step 17

Go to Step 6

6

  1. Start the engine.
  2. Place the mode switch in the FLOOR position.

Does the A/C compressor operate?

--

Go to HVAC Compressor Clutch Does Not Disengage

Go to Step 7

7

  1. Observe the drive shaft of the air temperature actuator.
  2. Place the air temperature switch from the coldest position to the warmest position.

Does the air temperature actuator drive shaft rotate at all?

--

Go to Step 8

Go to Step 9

8

Inspect the air temperature door and the air temperature actuator for the following conditions:

    • Misaligned air temperature actuator--Refer to Temperature Valve Actuator Replacement .
    • Broken or binding linkages or air temperature door
    • Obstruction that prevents the air temperature door from operating within its full range of motion
    • Missing seals to the air temperature door
    • Misaligned seals to the air temperature door

Did you find and correct the condition?

--

Go to Step 17

Go to Step 9

9

Test the ignition 3 voltage circuit of the air temperature actuator for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 10

10

Test the ground circuit of the air temperature actuator for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 11

11

Test the air temperature door control circuit of the air temperature actuator for an open, high resistance, short to ground, or short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 12

12

Important:: Ensure that the HVAC control assembly connector is connected during this step in order to avoid misdiagnosis.

  1. Turn ON the ignition, with the engine OFF.
  2. Measure the voltage from the air temperature door control circuit of the air temperature actuator to a good ground.
  3. Place the air temperature switch from the coldest position to the warmest position.

Does the voltage measure within the specified values with a smooth transition between COLD and HOT?

0-12 V

Go to Step 13

Go to Step 14

13

Inspect for poor connections at the harness connector of the air temperature actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 15

14

Inspect for poor connections at the harness connector of the HVAC control assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 17

Go to Step 16

15

Replace the air temperature actuator. Refer to Temperature Valve Actuator Replacement .

Did you complete the replacement?

--

Go to Step 17

--

16

Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement .

Did you complete the replacement?

--

Go to Step 17

--

17

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2