The ambient air temperature sensor is a variable resistor interfaced to the body control module (BCM). The BCM monitors the ambient air temperature sensor. The ambient air temperature sensor is a 2-wire negative temperature coefficient thermistor. The BCM applies 5 volts to an internal input resistor connected to the signal circuit of the ambient air temperature sensor. The BCM also provides the ground to the ambient air temperature sensor through the low reference circuit. When the ambient air temperature is cold, the sensor resistance is high and the signal voltage is high. When the ambient air temperature is hot, the sensor resistance is low and the voltage signal is low. The BCM provides the logic for reading the sensor, filtering the data and transmitting this information via the serial data circuit to the driver information center (DIC) 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 serial data signals are ultimately generated. An unfiltered value and a filtered value for use by the DIC 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.

Schematic Reference

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

Scan Tool Data List

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

⇒	If greater than 1 ohm, test the low reference 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 greater than 4.7 volts.

⇒	If less than 4.7 volts, test the ambient air temperature sensor signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3-amp fused jumper wire between the ambient air temperature sensor signal circuit terminal A and ambient air temperature sensor low reference circuit terminal B. 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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.