Intake Air Temperature (IAT) Sensor

The Intake Air Temperature (IAT) sensor contains a thermistor, a semi-conductor device that changes resistance based on temperature. The IAT sensor is in the air intake passage of the engine air induction system as a part of the Mass Air Flow (MAF) assembly. The ECM monitors changes in voltage on the signal wire due to resistance variations as the intake air temperature changes.

When the intake air is cold, the sensor resistance will be high, and the signal voltage will be near 5 V. When the intake air is warm, the sensor resistance will become low, and the signal voltage will read closer to 0 V.

The Scan tool displays the temperature of the incoming air, not the voltage on the signal circuit. This should be near ambient air temperature when the engine is cold. The temperature should rise as the underhood temperature increases. If the engine has not been run for several hours, the IAT and ECT should read close to the same value.