Outside Air Temperature Display Inaccurate or Inoperative

Outside Air Temperature Display Inaccurate or Inoperative

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The outside air temperature sensor is a variable resistor interfaced to the body control module (BCM). The BCM provides the logic for reading the sensor, filtering the data and transmitting this information via the GM LAN Low Speed Bus to the instrument panel cluster (IPC) for display. The temperature is sent to the IPC in Degrees Celsius. The IPC is responsible for displaying the temperature and converting to Degrees Fahrenheit if necessary. Two GM LAN Low Speed Bus signals are ultimately generated. An un-filtered value and a filtered value for use by the IPC display. The BCM also provides the sensor out-of-range detection and compensates for engine temperature by utilizing vehicle speed and engine off time duration. The algorithm for all messages is executed at a rate of once every 1 second.

Diagnostic Aids

The temperature reading involves an elaborate process involving outside air temperature, vehicle speed, and engine off time. To avoid confusion of an inaccurate temperature reading, review the outside air temperature description and operation. Refer to Driver Information Center (DIC) Description and Operation.

Circuit/System Testing

1. Ignition OFF, disconnect the ambient air temperature sensor.
2. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit and ground.

• If greater than 1 ohm, test the ground circuit for an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, verify the scan tool Ambient Air Temp. Sensor parameter is between 4.7 volts and 5.3 volts.

• If less than 4.7 volts, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

• If greater than 5.3 volts, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.

4. Install a 3-amp fused jumper wire between the signal circuit and ground. Verify the scan tool Ambient Air Temp. Sensor parameter is less than 0.4 volt.

• If greater than 0.4 volt, test the signal circuit for an open/high resistance. If the circuit tests normal replace the BCM.

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

* Ambient Air Temperature Gage Sensor Replacement
* Control Module References for BCM replacement, setup, and programming Verification Tests