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 co-efficient 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 low reference circuit to the ambient air temperature sensor. 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 signal voltage is low. The BCM provides the logic for reading the ambient air temperature sensor, filtering the data and transmitting the information via the serial data circuit to the driver information center (DIC) for display in the radio. The temperature is sent to the DIC in Degrees Celsius. The radio is responsible for displaying the temperature and converting to Degrees Fahrenheit. Two serial data signals are ultimately generated. An un-filtered 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 BCM detects that the ambient air temperature is 0.4 volt or more than 4.8 volts.

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 sensor low reference circuit terminal B and ground.

⇒	If greater than the specified value, 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 Temperature Sensor parameter is greater than 4.7 volts.

⇒	If less than the specified value, test the signal circuit terminal A 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 the low reference circuit terminal B. Verify the scan tool Ambient Air Temperature Sensor parameter is less than 0.4 volt.

⇒	If greater than the specified value, 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.