Air Temperature Sensor ( Ambient / Intake ): Description and Operation

PURPOSE
The Intake Air Temperature (IAT) sensor is a thermistor which changes value based on the temperature of air entering the engine. The IAT sensor signal is used in starting and running fuel control calculations.

OPERATION
Low temperature produces a high resistance (100,000 ohms at -40°C / -40°F), while high temperature causes low resistance (70 ohms at 130°C / 266°F). The Powertrain Control Module (PCM) supplies a 5 volt signal to the sensor through a resistor in the PCM and measures the voltage. The voltage will be high when the intake air is cold, and low when the air is hot. By measuring the voltage, the PCM calculates the incoming air temperature.

A fault in the IAT sensor circuit will set either a Diagnostic Trouble Code (DTC) 23 or DTC 25.