Air Temperature Sensor ( Ambient / Intake ): Description and Operation

Air Charge Temperature (ACT) Sensor:

The Air Charge Temperature (ACT) sensor is threaded into the intake air passage with a sensing element extending into the air chamber.
The ACT sensor is a negative temperature coefficient sensor, meaning that as the temperature of the sensor increases, the resistance will decrease. As the resistance value changes, the signal sensed by the Electronic Control Assembly (ECA) will also change. The ECA reads the varying sensor resistance and determines the air charge temperature, using this information to optimize the air/fuel mixture.
The ACT sensor will also set a fault code when the ECA determines the output signal to be out of the normal operating range.