Intake Air Temperature (IAT) Sensor

The Intake Air Temperature (IAT) sensor contains a semiconductor device that changes resistance based on temperature (a thermistor). The IAT sensor is located within the mass air flow sensor. The IAT sensor has a signal circuit and a ground circuit. The ECM applies a voltage of about 5.0 volts on the signal circuit to the sensor. The ECM monitors changes in this voltage caused by changes in the resistance of the sensor in order to determine the intake air temperature.

When the intake air is cold, the sensor (thermistor) resistance is high, and the ECM's signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the ECM will sense a high signal voltage (low temperature). When the intake air is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the ECM to sense a low signal voltage (high temperature).

The scan tool displays the temperature of the air entering the engine. This reading should be close to the ambient air temperature when the engine is cold. The temperature reading should rise as the underhood temperature increases. If the engine has not been run for several hours (overnight) the IAT sensor temperature and the engine coolant temperature should be similar.