The MAF sensor works according to the hot wire principle.
The MAF sensor is used exclusively to regulate exhaust gas recirculation EGR (closed control loop) and not for fuel metering, as is the case in petrol engines.’
Effects of faults
If the signal from the MAF sensor fails then the EGR rate is regulated using an emergency running map.
However, this means that the EGR rate is not regulated closely to the operating limit, and as a result is outside the limits.
Diagnosis
The monitoring system checks:
โข the sensor for short circuit to ground/battery and open control loop.
โข the sensor for illogical voltage jumps (illogical voltage jumps could indicate a loose connection, for example).
โข whether the output signal of the MAF sensor corresponds to the map data.