The crankshaft sensor picks up the position of the crankshaft using a sensor wheel with various recesses that is bolted onto the crankshaft. On the S54 engine, it works according to an inductive principle and is fitted on the gearbox directly in the proximity of the segment wheel.
It is necessary for the fully sequential injection system (fuel injection takes place individually for each cylinder at the specific firing point).
A permanent magnet in the sensor produces a magnetic field. A conductor with current flowing through it is located in this magnetic field. An electric voltage dependent on the strength of the magnetic field is produced in this conductor perpendicular to the current and perpendicular to the magnetic field. The magnetic field in the sensor is varied by the crankshaft sensor wheel and its apertures rotating passed the sensor. The teeth and gaps on the sensor wheel can be recognised by means of the voltage.
The number of teeth between the occurrence of two gaps is monitored continuously. The signals of the camshaft sensor are also compared with the signal of the crankshaft sensor and they must lie within specified limits.
The crankshaft signal can also provide information on the individual cylinder combustion misfires, as the monitoring for combustion misfires is based on the periodical acceleration of the crankshaft. This acceleration depends on the driven system. If no acceleration can take place at a defined moment, a combustion misfire can be the cause, as the rough operation values stored in the control unit are exceeded.