Iat sensor

Intake Air Temperature Sensor (IAT)

The IAT sensor allows the automotive computer to correct the injection timing of the ignition system according to the density of air entering the combustion chamber. This measurement is immediate from a cold start and as the engine begins to warm up. The IAT sensor sends the thermistor signal and the ECU regulates the amount of fuel injected for best performance.

What is the Intake Air Temperature Sensor?

The IAT sensor itself is a thermistor or thermal resistor that not only senses the temperature but adjusts to a varying degree. The higher the heat, the lower the resistance of the IAT. This sensor works in conjunction with the ECU and determines the temperature of the air entering the engine. Also involved is the Manifold Absolute Pressure Sensor (MAP) which signals changes in pressure, and air density and adjusts the amount of fuel required.

The incoming air is less dense when the temperature rises. For this reason, the air entering the manifold is less dense. When the air is cold, more volume needs to be burned. On vehicles that are also equipped with a MAP sensor, the IAT is close to the air intake duct.

On cars with Mass Air Flow Sensor, the IAT is part of the MAF sensor. In addition, the intake air temperature sensor is connected to the THA terminal on the ECM. The IAT senses the natural temperature at a cold start and continues the cycle of sensing the hot air by the incoming gases to the engine.

What is the Intake Air Temperature Sensor used for?


The engine control unit (ECU) can calculate the airflow into the combustion chamber. It does this thanks to this sensor, the ECM determines the cold engine start by comparing signals from the ETC and the IAT.

These two instruments should be within 8°C to 10°C of each other. Thus, the ECM understands that the car is cold and adjusts the temperature parameters at start-up.

How does the IAT Sensor work?

The IAT sensor checks the temperature of the incoming air to the engine and sends the corresponding signal to the computer to adjust the composition and timing of the injection pulse. The strategy to establish the engine cold start is the comparison made by the ECM between the signals from the IAT and ETC sensors.

This is very useful when using diagnostic monitors such as the EVAP system, which captures vapors from the gasoline tank to prevent escape to the environment.

Basically, the temperature sensors perform the same operations as follows:

  • The voltage signal from IAT to powertrain control (PCM).
  • Decreases voltage as sensor temperature warms up.
  • Resistance drops as temperature drops.
  • The voltage signal drops as resistance changes

There are fixed values on the IAT resistor. The electronic control module (ECM) provides 5 volts to the circuit, to measure the voltage variables between the temperature sensor and fixed value resistor.

As the Sensor cools, its resistance and voltage signal is high. As the sensor warms up, the signal voltage and resistance decrease. The ECM can determine intake air, exhaust gas, and coolant temperature.

Intake Air Temperature Sensor Location

The IAT sensor is almost always located on the throttle body, threaded into the intake manifold or rear air cleaner assembly. IAT sensors have a ground wire on the ECU, terminal E2. The IAT is in the thermistor category. You can find out the exact location of the IAT Sensor by acquiring the car's electrical diagrams.

Types of Intake Air Temperature Sensor

There are two types of IAT Sensor:

Manifold Absolute Pressure IAT

The Manifold Absolute Pressure Sensor measures the absolute pressure in the intake manifold. Its basis of operation is in the EGR valve which recirculates some exhaust gases back to the cylinders to reduce nitrogen oxide (NOX) emissions. The absolute pressure sensor control unit and the crankshaft sensor generate a signal to the injectors.

Frequency-variable IAT

This serves two purposes: to measure barometric pressure and the absolute pressure of the intake manifold. The sensor informs the control unit about the barometric pressure when the vehicle is switched off and the throttle valve is fully open. When there are altitude variations, it corrects the injector signal. In this case, the formula is barometric pressure minus vacuum or suction coming from the cylinders.

Its check passes through a value above 3.0 volts, but the tensional pressure that indicates its operation does not vary. Its normal characteristics are:

  • The frequent output signal translates between 90 and 160 hertz.
  • The supply voltage is over 5.0 volts.
  • The ground tap should be no more than 0.08 volts.

Common Intake Air Temperature Sensor Faults

Any IAT Sensor failure is recognized by three problems described below:

  • Short circuit: when the wires coming out of the sensor connector are shorted, due to damage to the insulation and the copper is exposed.
  • Open circuit: High resistance means too cold a temperature for the type of sensor.
  • Fault: Voltage values are not adequate.

Some of the faults are made evident by:

  • Slow start with a cold engine.
  • Check Engine light warning.
  • Loss of power.
  • High fuel consumption.
  • Increased emission of pollutants (CO).
  • High acceleration.
  • Poor ignition timing control by the computer.

How to test if the IAT Sensor is working?

The first thing you can do is a visual check, following the steps below:

  • Check the connectors associated with this sensor, they should be tight and free of sulfate.
  • The wiring should be free of splices.
  • Then to know how to test the temperature sensor, use the multimeter. Check the connector for voltage. It should measure 5 volts. In addition, you can test the grounding pin and see if the circuit is not open.

Also, you can test the sensor correctly with simple methods:

  • With a hairdryer heat the tip of the IAT Sensor.
  • Use the test indicator to measure the heat.
  • Verify that the resistor has a fixed value or is open. If this is the case, the sensor must be replaced.

Intake Air Temperature Sensor OBD2 Codes

OBD2 codes are alpha-numeric descriptions for detecting pollutant gases emitted into the environment by motor vehicles. Upon failure of the IAT Sensor, the codes report the following meaning:

  • P0112: Input below the estimated range. If it is less than 0.18 volts it generates the fault.
  • P0113: Indicates high input to the circuit. May be caused by damage to the wiring or the sensor itself.
  • P0127: Air temperature or voltage is too high.

How to clean the Intake Air Temperature Sensor?

Like any automotive instrument, the IAT sensor requires inspection and maintenance. Among the aspects to be covered are:

  • Review at every 45,000 kilometers tune-up.
  • Verify that the wiring is in good condition.
  • The harness should not present breaks, cracks, rust, or sulfate.
  • Remove dirt on the sensor tip with a rag and quick-drying spray cleaner.
  • Do not ignore the fault signals according to OBD2 codes.
  • Follow the instructions in the manual to prolong its service life.

In summary, the IAT sensor performs a very important function for the good performance of the engine. It is a part that contributes to the control of environmentally harmful engine emissions. Therefore, you must keep an eye on its maintenance and protect its good condition. This way you will avoid the headache of having to repair all the failures that come with not keeping it in good shape.


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