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

Intake Air Temperature Sensor:

The Intake Air Temperature (IAT) (previously MAT) sensor, is a thermistor whose resistance changes as a function of the temperature of air entering the engine. When the temperature is low, the resistance is high. Resistance decreases as the temperature increases. The voltage will be high when the incoming air is cold, and low when the air is hot. The IAT sensor is a two wire sensor that receives a 5.0 volt signal from the PCM through a resister in the PCM and measures voltage output. By measuring the voltage, the PCM calculates the incoming air temperature. The IAT sensor is also used to control spark timing.

ED23 displays temperature of the air entering the engine and should read close to ambient air temperature when engine is cold, and rise as underhood temperature increases. If the engine has not been run for several hours the IAT and coolant temperatures should read close to each other. A failure in the IAT sensor circuit should set a code 23 or 25.