Intake Air Temperature (IAT) Sensor
A sensor that measures the temperature of the air entering the engine, allowing the engine computer to adjust fuel delivery.
The Intake Air Temperature (IAT) sensor is an engine management component that measures the temperature of the air entering the engine intake manifold. Because the density of air changes with its temperature (cold air is denser than hot air, requiring more fuel for proper combustion), the Engine Control Unit (ECU) relies on IAT data to calculate the exact mass of air entering the engine and adjust fuel delivery and ignition timing accordingly.
The IAT sensor is typically a thermistor, which is a resistor that changes its electrical resistance based on temperature. It is usually located inside the air intake duct between the air filter housing and the throttle body, or integrated directly into the Mass Air Flow (MAF) sensor or Manifold Absolute Pressure (MAP) sensor assembly. The ECU sends a reference voltage to the sensor and monitors the voltage drop to determine the incoming air temperature.
If the IAT sensor fails, it can send inaccurate temperature data or no data at all to the ECU. This will cause the ECU to default to a pre-programmed safe value, which can lead to an incorrect air-fuel ratio. Symptoms of a bad IAT sensor include poor fuel economy, rough idling, engine hesitation during acceleration, hard starting in cold weather, and a Check Engine Light with stored trouble codes (like P0113 or P0112).
Testing an IAT sensor involves measuring its resistance at different temperatures using a digital multimeter and comparing the readings to the manufacturer's specifications. If the sensor is found to be out of range, it is easily replaced by unplugging the electrical connector and swapping out the sensor unit.