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 incoming air is cold, and low when the air is hot. By measuring the voltage, the PCM calculates the incoming air temperature.

If the engine has not been run for several hours (overnight) the IAT sensor temperature and engine coolant temperature should read close to each other. A failure in the IAT sensor circuit should set Diagnostic Trouble Code (DTC) 23 or DTC 25.