Hot film mass air flow sensor, component description

P07.07-2065-04

B2/5 Hot film mass air flow sensor

Location

The hot film mass air flow sensor is located at the top of the air filter housing.

Task

The hot film mass air flow sensor measures the intaken air mass and air temperature. These values are required by the motor electronics control unit (N3/10) for calculation of the correct injection quantity.

Function

The hot film mass air flow sensor is a thermal load sensor and detects the air mass and air temperature drawn in by the engine. The electrically heated body projecting into the intake air flow is cooled down by the air flow. A control circuit measures the hot flow, that the heated body assumes a particular temperature via the intake air temperature.

The respective hot stream is thus a measurement for the mass air flow. The air density is included in this measuring method, as it affects the cooling down of the heated body. Denser air (sea level) equals a larger air mass and results in faster cooling than the lower density air mass.

The larger the mass of intaken air, the higher the oxygen content and thus the quantity of fuel required. Failure of the hot film mass air flow sensor is compensated by the engine electronics control unit via the signals from the throttle valve actuator (M16/6) and the speed performance map saved in the motor electronics control unit.

 In the event of signal failure, the missing signals are compensated by the motor electronics control unit using the signals from the accelerator pedal sensor and a stored performance map.