GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

DEFINITION: Improper control response, set temperature requires frequent adjustment or changes by itself.

1

Did you perform the HVAC Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, perform the Recalibrate all Motors command in instrument panel module IPM Special Functions.
  4. With a scan tool, observe the current DTC list in the IPM.

Does the scan tool display any DTCs?

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Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

Inspect for a poor battery condition. Refer to Battery Inspection/Test in Engine Electrical.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 4

4

Visually inspect the following:

    • Stuck or intermittent sticking switch on the HVAC control module.
    • Stuck or intermittent sticking switch on the steering wheel controls.
    • Stuck or intermittent sticking switch on the personalization controls.

Did you find and correct the condition?

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Go to Step 22

Go to Step 5

5

Verify that the customer is using the correct key to enable personalization and is not inadvertently activating the steering wheel controls or right air temperature switch assembly.

Did you find and correct the condition?

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Go to Step 22

Go to Step 6

6

  1. Install a scan tool.
  2. Cover the sunload sensor assembly.
  3. Start the engine.
  4. Place the temperature switch in the 24°C (75°F) position.
  5. Place the right air temperature switch assembly in the neutral position.
  6. With a scan tool, observe the Right and Left Solar Sensor data parameters in the IPM Open/Short Data list.

Does the scan tool indicate that the Right and Left Solar Sensor data parameters are more than the specified value?

224 Counts

Go to Step 7

Go to Step 17

7

  1. Uncover the sunload sensor assembly.
  2. Direct a light source at the right and then the left side of the sunload sensor assembly.

Do the counts change similarly and correspond to the proper side of the sunload sensor assembly?

--

Go to Step 8

Go to Step 17

8

  1. Fully open all panel outlets.
  2. Place the temperature switch in the 24°C (75°F) position.
  3. Place the mode switch in the panel position.
  4. Set blower speed to illuminate 2 bars on the fan speed indicator.
  5. Place the right air temperature switch assembly in the neutral position.
  6. Inspect for airflow through the inside air temperature sensor by placing a 5 cm (2 in) square piece of paper over the sensor air inlet.

Does the paper stay in place?

--

Go to Step 9

Go to Step 16

9

  1. Turn OFF the ignition.
  2. Inspect the air temperature sensors for proper installation. Refer to the following procedures:

Did you find and correct the condition?

--

Go to Step 22

Go to Step 10

10

Inspect for poor connections at the following air temperature sensor harness connectors:

    • Upper right
    • Upper left
    • Lower right
    • Lower left

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 22

Go to Step 11

11

Test the resistance of the following air temperature sensors:

    • Upper right
    • Upper left
    • Lower right
    • Lower left

Refer to Sensor Resistance Table

Do the resistances measure near the Sensor Resistance Table values?

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Go to Step 12

Go to Step 21

12

Inspect for poor connections at the harness connector of the ambient air temperature sensor. 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 22

Go to Step 13

13

Test the ambient air temperature sensor resistance. Refer to Sensor Resistance Table .

Does the resistance measure near the Sensor Resistance Table value?

--

Go to Step 14

Go to Step 19

14

Inspect for poor connections at the harness connector of the inside air temperature sensor. 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 22

Go to Step 15

15

Test the inside air temperature sensor resistance. Refer to Sensor Resistance Table .

Does the resistance measure near the Sensor Resistance Table value?

--

System OK

Go to Step 20

16

Inspect for a blocked or disconnected aspiration hose.

Did you find and correct the condition?

--

Go to Step 22

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17

Inspect for poor connections at the harness connector of the sunload sensor assembly. 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 22

Go to Step 18

18

Replace the sunload sensor assembly. Refer to Sunload and Twilight Sentinel Sensor Replacement in Instrument Panel, Gages, and Console.

Did you complete the replacement?

--

Go to Step 22

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19

Replace the ambient air temperature sensor. Refer to Ambient Air Temperature Sensor Replacement .

Did you complete the replacement?

--

Go to Step 22

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20

Replace the inside air temperature sensor. Refer to Inside Air Temperature Sensor Replacement .

Did you complete the replacement?

--

Go to Step 22

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21

Replace the suspect air temperature sensor. Refer to the following procedures:

Did you complete the replacement?

--

Go to Step 22

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22

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 3