Intake Air Temperature Sensor
Intake Air Temperature (IAT) sensors and integrated MAF type, are thermistor devices in which resistance changes with temperature. See Fig 1 and Figure . Electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. Varying resistance affects voltage drop across sensor terminals and provides electrical signals to PCM corresponding to temperature. Thermistor type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in a series with sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus voltage drop across fixed resistor. IAT provides air temperature information to PCM. PCM uses air temperature information as a correction factor in calculation of fuel, spark and MAF. IAT sensor provides a quicker temperature change response time than ECT or CHT sensor.
Supercharged vehicles use 2 IAT sensors. Both sensors are thermistors. However, one is located before the supercharger at air cleaner for standard OBD-II cold weather input, while the second sensor (IAT2) is located after the supercharger in intake manifold. IAT2 sensor located after supercharger provides air temperature information to PCM to control border-line spark and to help determine intercooler (charge air cooler) efficiency.
Currently 2 types of IAT2 sensors are used on supercharged vehicles. A screw in type and an integrated type, which is part of Thermal Manifold Absolute Pressure (TMAP) sensor. See Fig 1 and Figure . TMAP sensor consists of an IAT thermistor and a Manifold Absolute Pressure (MAP) sensor. The thermistor portion of TMAP is used for IAT2 function and operates in the same manner as a non-integrated IAT2. For additional information on the TMAP, see THERMAL MANIFOLD ABSOLUTE PRESSURE SENSOR .