Theory Of Operation

WARNING: This page is about a different car, the 2016 Dodge Durango. However, it is still accessible from the selected car via links, so may be relevant.

The Ambient Air Temperature (AAT) Sensor is a variable resistor that functions as a normal two wire, 5 volt sensor. The BCM supplies the AAT Sensor with a 5-Volt reference and a filtered ground (return) 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. For the AAT Sensor diagnostic, the BCM internally monitors the voltage on the signal circuit, which is converted into a temperature reading. The AAT Sensor signal reading is a bussed message from the Body Control Module (BCM) to the Powertrain Control Module (PCM). If the voltage reads above the high calibrated threshold, or below the low calibrated threshold, a circuit high or low fault is set. The Ambient Air Temperature (AAT) Sensor rationality diagnostic runs under cold start conditions, following a start to run delay time and compares the outputs of the ambient, engine coolant and intake air temperature sensors. If the Engine Coolant and Intake Air Temperature Sensors agree and the Ambient Air Temperature Sensor does not agree, the Ambient Air Temperature Sensor is declared as irrational. If declared irrational a second comparison will be done after a short drive cycle.