Crankshaft Position and Engine Speed Sensor

Description
The engine speed and angular position is determined by use of a Siemens differential 'Hall Effect' sensor attached to the gearbox. The sensor picks up its signal from the reluctor ring within the gearbox which is rotating in front of the sensitive area of the sensor, the integrated circuit detects the magnetic field variations due to the passing of the teeth of the wheel and converts them into a digital signal.

The 'pulse train' generated by the 'switching' of the sensor is fed into the ECM which measures the time between teeth to calculate the engine speed. As there are some 'missing teeth' on the reluctor ring, by detecting the location of these teeth the ECM synchronises itself to the sensor enabling the determination of the angular position of the crankshaft. There are a total of 58 (60-2) teeth on the reluctor each of which are 6 degrees of engine crank apart where the missing 2 teeth denote 36 degrees after TDC.

There are two diagnostic checks on the output signal of this sensor: -
1. No teeth on the reluctor ring have been detected and a cam sensor signal is present.
2. The number of counted reluctor ring teeth is greater than the number of actual reluctor ring teeth.