IATSensor

Intake Air Temperature Sensor (IAT)

Group: Temperature and oil pressure

The IAT sensor measures the temperature of the air entering the engine. Cold air is denser, so the computer uses this value to correct the amount of fuel and the ignition timing. Some manuals call it MAT (manifold air temperature).

Contents

What does the IAT sensor do?

Like the ECT, it is an NTC thermistor: its resistance drops as the temperature rises. The computer corrects injection for air density and pulls timing when the air is very hot, to avoid knock. Turbo engines usually have a second sensor after the intercooler (sometimes called MAT or charge air temperature sensor) to monitor how well the air is being cooled.

Where is it located?

Built into the MAF sensor, in the air filter box, in the intake duct or in the intake manifold. On turbo engines, also after the intercooler.

Signal type and reference values

  • 2 wires: signal with a 5 V reference and ground (or shared with the MAF).
  • Approximate resistance: 2,000 to 3,000 ohms at 20 °C (68 °F); about 300 ohms at 80 °C (176 °F).
  • While driving, the IAT usually reads between ambient temperature and 20 to 30 °C above it.

Values are a guide only: always check the manufacturer's data for your engine.

Symptoms of a bad IAT sensor

  • Hard starting and rough idle when cold.
  • Slightly higher consumption or a small loss of power.
  • Pinging in hot weather (if it reports colder air than reality).
  • Codes P0110 to P0114.

How to test the IAT sensor step by step

  1. With the engine cold after several hours off, the IAT should match the ambient temperature and the ECT.
  2. A fixed reading of -40 °C means an open circuit; a fixed, very high reading (over 120 °C) means a short to ground.
  3. Measure the sensor resistance at room temperature, then warm it gently with a hair dryer: the resistance should drop.
  4. Check for the 5 V reference and ground at the connector.

Trouble codes related to the IAT sensor

Frequently asked questions about the IAT sensor

Are the IAT and the MAT the same sensor?
They measure the same thing (air temperature) at different points. The IAT usually sits before the engine or inside the MAF; the MAT is in the manifold or after the intercooler.
Can a bad IAT sensor stop the car from starting?
Rarely. It usually causes a slightly wrong mixture, higher consumption or hard cold starts, but the engine keeps running.

Updated September 25, 2026. Values are a guide only: always confirm them in the service manual for your engine.

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