The ambient air temperature sensor is a variable resistor interfaced to the inside rearview mirror via the ambient air temperature sensor signal circuit and low reference circuit. The mirror provides the logic for reading the ambient air temperature sensor, filtering the data and displaying the outside air temperature. A warmer outside air temperature results in a lower ambient air temperature sensor resistance. Temperature reading exceeding 62°C (143°F) is out of the mirror's temperature range and will not be displayed. When the temperature reading exceeds 62°C (143°F), "SC" is displayed in the mirror temperature display. A colder outside air temperature results in a higher ambient air temperature sensor resistance. Temperature reading lower than -40°C (-40°F) is out of the mirror's temperature range and will not be displayed. When the temperature reading is lower than -40°C (-40°F), "OC" is displayed in the mirror temperature display. In colder temperatures such as 3°C (37°F) or below, the mirror displays "ICE" when the ignition is first turned on. The mirror temperature display toggles between "ICE" and the actual outside temperature until the temperature update process is complete. If the ambient air temperature sensor is opened or shorted, the temperature displayed is either a cold or hot extreme. An open ambient air temperature sensor displays as "OC" and an ambient air temperature shorted to ground displays as "SC".

The following table will be used to measure the resistance of the sensor and compare it with the actual ambient temperature. The mirror's temperature accuracy should be within 5 degrees of the actual temperature. The actual temperature should not be taken from a radio station, a sign displaying the temperature, etc. A temperature measuring tool such as a thermometer should be used. Some temperature measuring tools may be within 5 degrees of the actual temperature. Make sure to consult the manufacturer for the accuracy of the tool. This comparison can make the mirror seem off by 5-10 degrees of the actual temperature when it is not.

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 low reference circuit and ground.

⇒	If greater than 1 ohm, test the low reference circuit for an open/high resistance.

3. Ignition ON, verify the inside rearview mirror displays "OC".

⇒	If the inside rear view mirror temperature display does not display "OC", test the ambient air temperature sensor signal circuit for a short to ground. If the circuit tests normal, replace the inside rearview mirror.

4. Ignition ON, install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ambient air temperature sensor. Verify the inside rearview mirror displays "SC".

⇒	If the inside rearview mirror temperature display does not display "SC", test the signal circuit of the ambient air temperature sensor for a short to voltage or an open/high resistance. If the circuit tests normal, replace the inside rearview mirror.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.