Ambient Air Temperature Sensor
The Ambient Air Temperature (AAT) sensor is a Negative Temperature Coefficient (NTC) thermistor. The AAT sensor allows the Powertrain Control Module (PCM) to monitor the temperature of the air around the vehicle. The PCM uses the AAT sensor input for a number of functions, including engine cooling fan control. The PCM also transmits the ambient air temperature on the FlexRay bus for use by other control modules.
The AAT sensor is installed in the left door mirror, with the bulb of the sensor positioned over a hole in the bottom of the mirror casing.
The PCM supplies the sensor with a 5V reference voltage and a ground, and translates the return signal voltage into a temperature value.
If there is a fault with the AAT sensor, the PCM calculates the AAT from the temperature inputs of the Mass Air Flow and Temperature (MAFT) sensors. If the AAT sensor and the temperature inputs of the MAFT sensors are all faulty, the PCM adopts a default ambient temperature of 25°C (77°F).