The Intake Air Temperature (IAT) sensor reads the temperature of the air entering the engine. Knowing this information is important because the greater the amount of intake of air, the higher the combustion temperatures. These combustion temperatures affect nitrogen oxide emissions by increasing them.
In order to prevent these high temperatures from causing combustion temperatures, it is necessary that the intake air pipe is intact, thus allowing air that is not in the engine compartment, fresh air, to enter the engine. The IAT sensor uses a thermistor or thermometer to measure the air temperature. This thermistor receives a 5-volt reference and ground signal. It should be noted that when the air temperature is cold, the resistance of the thermistor is high and the opposite occurs when the temperature is warmer.
This variation in resistance directly affects the reference voltage, which informs the PCM of the incoming air temperature. If the PCM detects that the temperature is high, but the engine temperature is actually low, the P0097 OBDII diagnostic code is set, in addition to illuminating the Check Engine light.