The HVAC control module monitors the ambient air temperature sensor with a low reference circuit and 5-volt signal circuit. The HVAC control module monitors the voltage drop across the sensor, which is proportional to temperature. When the ambient air temperatures are cold, the resistance of the sensor is high and the voltage signals are high. When the ambient air temperatures are hot, the resistance of the sensors is low and the voltage signals are low. The HVAC control module converts the voltage value to a temperature value of Celsius and Fahrenheit that will be displayed by the driver information center (DIC).

The ignition is turned ON.

The HVAC control module uses a default air temperature value for compressor clutch operation.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for Scan Tool Information

Ignition ON, observe the ambient air temperature sensor. The reading should be between -35°C (-39°F) and 85°C (185°F) and change with ambient air temperature changes.

Important: If the ambient air temperature sensor is in temperatures below 2°C (35°F) the compressor clutch will be disabled until the vehicle is driven above 45 mph (72 km/h), the ignition is OFF for more than 3 hours or an instant OAT update is performed.

Important: An instant OAT update must be performed by pressing the A/C and Recirc buttons at the same time before and after the system has been serviced to update the filtered ambient air temperature sensor circuit and convert the A/C permission from withheld to granted.

1. Ignition OFF, disconnect the harness connector at the ambient air temp sensor.
2. Ignition OFF, test for less than 10 ohms of resistance between the low reference circuit terminal B and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, verify the scan tool Ambient Air Temp Sensor parameter is less than -35°C (-39°F).

⇒	If greater than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module.

4. Install a 3 A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool Ambient Air Temp Sensor Raw parameter is greater than 85°C (185°F).

⇒	If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

Important: An instant OAT update must be performed to grant A/C permission after testing or replacing the ambient air temperature sensor.

5. If all circuits test normal, test or replace the ambient air temp sensor.

Important:  Sensor Resistance Table for this test. A thermometer can be used to test the sensor off the vehicle in warn and or cold water.

1. Test the ambient air temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
2. Compare the readings with the Temperature VS Resistance table and verify that the resistance is within 5 percent of the specification.

⇒	If not within the specified range, replace the sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.