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

Intake Air Temperature (IAT) Sensor:

The Intake Air Temperature (IAT) sensor is a thermistor which changes value based on the temperature of air entering the engine. Low temperature produces a high resistance (100,000 ohms at -38°C/-39°F). A high temperature causes low resistance (70 ohms at 130°C/266°F). The PCM supplies a 5.0 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. The IAT sensor signal is used to adjust spark timing according to incoming air density.

The scan tool displays temperature of the air entering the engine, which should read close to ambient air temperature when the engine is cold. The temperature should rise as underhood temperature increases. 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. If the PCM detects a malfunction in the IAT sensor circuit, one or more of the following DTCs will set:
^ DTC P0112 IAT Sensor Circuit Low Voltage
^ DTC P0113 IAT Sensor Circuit High Voltage
^ DTC P1111 IAT Sensor Circuit Intermittent High Voltage
^ DTC P1112 IAT Sensor Circuit Intermittent Low Voltage