300SE (140.032) L6-3.2L (104.990) (1992)
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Air Flow Meter/Sensor: Description and Operation
Air Mass Sensor
Air Mass Sensor
PURPOSE AND LOCATION
The air mass sensor (B2/2), located on LH side of engine, sends a signal (current) to the LH control module. The control module can now
calculate the air mass entering the engine and adjust fuel injection duration as needed. The air mass sensor is of the hot-wire sensor type. Factors
such as ambient temperature, humidity and pressure (altitude) are taken into consideration with this type of air sensor.
OPERATION
The measurement sensor (inside the meter housing) consists of a wire (hot-wire) which is maintained at a temperature 180°C (356°F) higher than
the air entering the engine. As the air mass passes over the hot-wire, wire resistance decreases and more current is required to maintain the correct
temperature. The amount of current required is used to calculate the air mass entering the engine. When the engine is turned off, any dirt on the
wire is burned off electrically by a one second burn off cycle that heats the wire to 1000°C (1800°F). Any dirt remaining on the hot-wire can cause
it to sent a faulty signal to the LH control module.
LIMP HOME MODE
If the air mass sensor fails, the LH control module goes into a "limp home mode". The control module uses the intake manifold pressure sensor
signal (via controller area network) to operate the engine. This enables the vehicle to be driven to the next available repair shop.
