Theory Of Operation

The Ambient Air Temperature (AAT) Sensor reading is a bussed message from the Body Control Module (BCM) to the Powertrain Control Module (PCM). The AAT Sensor is a variable resistor that functions as a typical two wire sensor. The BCM supplies a 5 volt reference and a ground to the sensors low reference signal circuit. When the ambient air temperature is low, the sensor resistance is high. When the ambient air temperature is high, the sensor resistance is low.

If during normal operation the AAT Sensor voltage goes above a calibrated maximum voltage threshold or below a calibrated minimum voltage threshold, the PCM will set a circuit fault. The PCM also does a plausibility check of the input signals of the Ambient Air, Engine Coolant and Intake Air Temperature Sensors under cold start conditions.