Intake Air Temperature Sensor (IAT)

Intake Air Temperature Sensor (IAT) monitors the temperature of the air entering the engine. (on the GM 8.1L this sensor inside the MAF sensor) The engine computer (PCM) needs this information to estimate air density so it can balance air/fuel mixture. Colder air is more dense than hot air, so cold air requires more fuel to maintain the same air/fuel ratio. The PCM changes the air/fuel ratio by changing the length (on time) of the injector pulses.

The air temperature sensor is a thermistor, which means its electrical resistance changes in response to changes in temperature. It works the same as a coolant sensor. The PCM applies a reference voltage to the sensor (usually 5 volts), then looks at the voltage signal it receives back to calculate air temperature. The return voltage signal will change in proportion to changes in air temperature. Most air temperature sensors are negative temperature coefficient (NTC) thermistors with high electrical resistance when they are cold, but the resistance drops as they heat up. However, some work in the opposite manner. They are positive temperature coefficient (PTC) thermistors that have low resistance when cold, and increase in resistance as they heat up. The changing resistance of the sensor causes a change in the return voltage back to the PCM. 

CAUSES OF FAILURE

An air temperature sensor can sometimes be damaged by:

Backfiring in the intake manifold

Carbon and oil contamination inside the intake manifold can also coat the tip of the sensor, making it less responsive to sudden changes in air temperature.

The air temperature sensor itself may also degrade as a result of heat or old age, causing it to respond more slowly or not at all.

Sensor problems can also be caused by poor electrical connections at the sensor. A loose or corroded wiring connector can affect the sensor’s output, as can damaged wiring in the circuit between the sensor and PCM.