Bosch Motronic - Component Datasheet

Intake Air Temperature Sensor (G42)

Located on the rear of the intake manifold, near the throttle valve body, the intake air temp. sensor (shortened to IAT) provides another important input to the ECU which is used to adapt ignition timing, knock regulation and boost pressure.

On the 3B engine, boost pressure is reduced with increases in air temperature. This makes a 3B more powerful on cold winter drives than hot summer days.

On the ABY engine, so as to provide a consistent engine performance regardless of the weather, the IAT actually permits HIGHER boost in warm air conditions than cold air. The reason for this is to keep the engine performance consistent whatever the temperature. However, in excessively high air temperatures the ECU actively reduces boost pressure to prevent knocking.

The thermistor device within G42 has a positive temperature coefficient (PTC) which is a fancy way of saying that its resistance increases with temperature. The choice of a PTC component is no accident - should G42 fail or be disconnected then the ECU is fooled into seeing a high temperature (of approx 40 degrees C). On the 3B this means boost reduction, but on the ABY it can give a boost increase of approx 0.2bar (compared to what the IAT would ask the ECU to do on a cold day).

NOTE - If replacing the IAT on the 3B engine that its not fitted with a modular 2-pin connector like the ABY and RS2. You need to order up 1 x 443-906-232 connector as well.