Outside Air Temperature Display Inaccurate or Inoperative

OUTSIDE AIR TEMPERATURE DISPLAY INACCURATE OR INOPERATIVE

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

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 GMLAN 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 GMLAN 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.

CIRCUIT/SYSTEM TESTING
1. Ignition OFF, disconnect the ambient air temperature sensor.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the low reference circuit and ground.
- If greater than 1.0 ohm, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Ambient Air Temp. Sensor parameter is greater than 4.7 volts.
- If less than 4.7 volts, test the signal circuit for a short to ground.
4. Ignition ON, 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 volts.
- If greater than 0.4 volts, test the signal circuit for an open/high resistance. If the circuit tests normal replace the BCM.
- If the scan tool parameter is normal, replace the ambient air temperature sensor.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

- Ambient Air Temperature Gage Sensor Replacement
- Control Module References for BCM replacement, setup, and programming.