GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The HVAC control module monitors the outside ambient air temperature via an ambient air temperature sensor. When the air is cold, the sensor resistance and signal voltage are high. When the air is warm, the sensor resistance and signal voltage are low.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The HVAC control module detects the signal circuit is less than 0.09 V (5 counts) or greater than 4.90 V (250 counts).

Action Taken When the DTC Sets

A default value will be used for the sensor data by the HVAC control module. The actual sensor reading will be displayed on the scan tool in the HVAC data list.

Conditions for Clearing the DTC

    • The DTC will become history if the HVAC control module no longer detects a failure.
    • The history DTC will clear after 50 fault free ignition cycles.
    • The DTC can be cleared with a scan tool.

Diagnostic Aids

If condition not present refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. Scan tool uses a default value, this will not give accurate reading of sensor value if open or short to ground.

  2. Tests for the possibility of a short to another 5 V reference circuit.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

  1. Turn OFF the ignition.
  2. Disconnect the ambient air temperature sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the ambient air temperature sensor signal circuit of the ambient air temperature sensor to a good ground.

Does the voltage measure near the specified value?

5 V

Go to Step 3

Go to Step 4

3

Measure the voltage from the ambient air temperature sensor signal circuit to the low reference circuit of the ambient air temperature sensor.

Does the voltage measure near the specified value?

5 V

Go to Step 6

Go to Step 5

4

Test the ambient air temperature sensor signal circuit of the ambient air temperature sensor for an open, high resistance, short to ground, or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

5

Test the low reference circuit of the ambient air temperature sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step  9

6

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 12

Go to Step 7

7

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

Does the resistance measure near the Sensor Resistance Table value?

--

Go to Step 8

Go to Step 10

8

  1. Disconnect the HVAC control module.
  2. Turn ON the ignition, with the engine OFF.
  3. Test the ambient air temperature sensor signal circuit of the ambient air temperature sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

9

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 12

Go to Step 11

10

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

Did you complete the replacement?

--

Go to Step 12

--

11

Important:: Perform the recalibration procedure for the HVAC control module.

Replace the HVAC control module. Refer to HVAC Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK