Ambient Air Temperature (AAT) Sensor
The Ambient Air Temperature (AAT) sensor is a NTC thermistor that allows the ECM to monitor the temperature of the air around the vehicle. The ECM uses the AAT sensor input for a number of functions, including engine cooling fan control. The ECM also transmits the ambient air temperature on the HS (High Speed) CAN (Controller Area Network) bus for use by other control modules.
The AAT sensor is installed in the left exterior mirror, with the bulb of the sensor positioned over a hole in the bottom of the mirror casing.
The ECM supplies the sensor with a 5 V reference voltage and a ground, and translates the return signal voltage into a temperature.
If there is a fault with the AAT sensor, the ECM calculates the AAT from the temperature inputs of the MAFT sensors. If the AAT sensor and the temperature inputs of the MAFT sensors are all faulty, the ECM adopts a default ambient temperature of 25 °C (77 °F).