Air Flow Meter/Sensor: Description and Operation

A hot film air mass sensor provides the air volume input for the MS41.1 Control Module. The operation of the sensor is the same as the hot film sensors for the Bosch engine management systems. The sensor receives operating power from the control module.

The hot film is heated to 300°C above the ambient temperature. As the intake air passes through the sensor, the film is cooled. The amount of current required to maintain the temperature of the heated film is used as a measurement of air volume being drawn in by the engine. The sensor produces a 1-5 VDC varying voltage signal, based on this heating current, that becomes the air volume input to the control module.

The air mass sensor is monitored as part of the OBD requirements for emission control. The signal from the air mass sensor is continuously monitored for faults while the engine is running. The monitoring parameters include:

- Upper and lower limits for the input voltage
- Plausibility of the input voltage signal (RPM versus Load signal)
- Open circuit

If a malfunction occurs, the MS41.1 control module will use the RPM and throttle position input signals as a replacement value (FAIL-SAFE) for engine loading. The Check Engine Lamp will illuminate when the criteria for OBD II monitoring is satisfied.