Intake Air Temperature (IAT) Sensor
The IAT sensor is a thermistor device in which resistance changes with temperature. The resistance of a thermistor decreases as the temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The IAT sensor provides air temperature information to the PCM. The PCM uses the air temperature information as a correction factor in the calculation of fuel, spark, and airflow.
The IAT sensor provides a quicker temperature change response time than the ECT or CHT sensor.
Currently there are 2 types of IAT sensors used, a stand alone and an integrated type. Both types function the same, however the integrated type is incorporated into the mass airflow (MAF) sensor or the turbocharger intake pressure and temperature (TCIPT) sensor instead of being a stand alone sensor.
Supercharged vehicles use 2 IAT sensors. Both sensors are thermistor type devices and operate as described above. One is located before the supercharger at the air cleaner for standard OBD and cold weather input, while the second sensor, intake air temperature 2 (IAT2), is located after the supercharger in the intake manifold. The IAT2 sensor provides air temperature information to the PCM to control spark and to help determine CAC efficiency.
The IAT2 sensor for speed density systems is centrally located on the intake manifold and is used to measure the intake manifold temperature. The PCM uses the information from the IAT2 sensor to determine the speed density air charge and provide input for various engine control functions. The IAT2 sensor for a speed density system is integrated with the manifold absolute pressure (MAP) sensor.