Intake Air Temperature Sensor
The intake air temperature (IAT) sensor is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and 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 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 air flow.
The IAT sensor provides a quicker temperature change response time than the ECT or CHT sensor.
Currently there are two design types of IAT sensors used, a stand alone\non-integrated type (Fig 1) and a integrated (Fig 2) type. Both types function the same, however the integrated type is incorporated into the Mass Air Flow (MAF) 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. However, one is located before the supercharger at the air cleaner for standard OBD II/cold weather input, while a second sensor (IAT2) is located after the supercharger in the intake manifold. The IAT2 sensor located after the supercharger provides air temperature information to the PCM to control border-line spark and to help determine intercooler efficiency.
Currently two types of IAT2 sensors are used. A non-integrated screw in type (Fig 1) and an integrated type, which is part of the Thermal Manifold Absolute Pressure (TMAP) sensor (Figure). The TMAP sensor consists of a IAT thermistor and a manifold absolute pressure (MAP) sensor. The thermistor portion of the TMAP is used for IAT2 function and operates in the same manner as a non-integrated IAT2. For additional information on the MAP portion of the TMAP, refer to the THERMAL MANIFOLD ABSOLUTE PRESSURE SENSOR description and operation.