Ambient Air Temperature Sensor
The AAT (ambient air temperature) sensor is a negative temperature coefficient (NTC) thermistor that allows the engine control module (ECM) to monitor the temperature of the air around the vehicle. The engine control module (ECM) uses the AAT input for a number of functions, including engine cooling fan control. The engine control module (ECM) also transmits the ambient temperature on the high speed controller area network (CAN) bus for use by other control modules.
The AAT sensor is installed on a bracket in the front bumper ducting, on the vehicle centerline.
The engine control module (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 engine control module (ECM) 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 mass air flow and temperature (MAFT) sensors are all faulty, the engine control module (ECM) adopts a default ambient temperature of 25 °C (77 °F).