Ambient Air Temperature (AAT) Sensor
The AAT sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical voltage signals to the powertrain control module (PCM) corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The AAT sensor provides ambient air temperature information to the PCM which is used for the temperature sensor correlation tests and controls the reductant heaters. The PCM also communicates the AAT information to all other modules on the controller area network (CAN).