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Intake Air Temperature Sensors (IAT) November 2012

IAT function The Intake Air Temperature sensor (IAT) has been utilised as an Engine Control Unit (ECU) input signal from the very first EFI systems to the currently used systems, as a requirement for calculating the Air Mass volume for the incoming air charge. This is, to assist in determining the correct engine fuel requirement to suit the operating air temperature.

What a lot of hot air It is important to maintain correct combustion mixtures during the extremely hot winds of summer as well as the freezing night winds of winter. The density of the air varies with the air temperature and with this, the amount of required fuel to ensure the correct mixture.

More now than in the past, the IAT plays a larger role in the mixture control due to the greater importance placed on controlling emission levels. That is, earlier vehicles with faulty IAT sensor causing a malfunction light to illuminate, with a fault code logged and little driveability problems to a Limp Home Mode condition on some of the later vehicles to ensure that the IAT circuit is rectified quickly.

Location, Location, Location Before we go any further, let us identify the IAT sensor unit as it may be integrated into various other Engine Management components.

1. Stand alone IAT sensor A two wire NTC (Negative Temp Coefficient) thermistor device that produces a resistance change in accordance to the exposed air temperature that it monitors. This may be located in the intake air tube between the air filter box and the throttle body.

Also may be threaded directly in the inlet manifold and is sometimes called a MAT sensor (Manifold Temp Sensor)

2. Integrated in the MAP sensor (T-MAP sensor) MAP sensors that are mounted directly on the inlet manifold may or may not integrate the IAT sensor. The MAP combination with the IAT may be identified by an extra 4th pin at the connector. That is a standard MAP sensor requires only 3 pins to function.

The 4th pin if fitted identifies the T-MAP sensor which utilises the common MAP sensor earth to complete the IAT circuit.

3. Integrated in the MAF (Mass Air Flow) sensor or AMM (Air Mass Meter) Multiple pin configurations may or may not indicate an integrated IAT sensor. The minimum circuit requirement for an Air Mass Sensor to function is 3 and units with this number of terminal configurations, do not incorporate an IAT sensor.

A greater number than 3 terminals on the AMM generally indicates the presence of an IAT sensor but there are exceptions and care must be taken when renewing these units to ensure the correct one is fitted.

4. Other typical areas In the Air Flow Meter housing (AFM) on earlier vehicles located at the inlet of the air flow chamber and also on the Karman Vortex AMM housing, located at the inlet of the air flow chamber

Testing the IAT sensor Generally, this unit would not be on the “to check” list unless a fault code was logged. A typical scanner will indicate the running intake air temperature at time of testing. It is important to note that a higher than normal IAT voltage would result in a richer mixture and would affect both emissions and fuel consumption.

Alternative Test methods - on standalone units

Alternative Test methods -on AMM units

Alternative Test methods – on T-MAP sensors

Note: Heating the IAT sensor with a hot air gun may assist in quicker diagnosis.

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