Camshaft Position (CMP) Sensor

Camshaft Position (CMP) Sensor

The sensor consists of an MRE (Magnetic Resistance Element). It is a permanent magnet with 2 special semiconductor resistors, which are connected in series with each other, as described in the picture above. The output signal is an analog sine curve which passes through an analog/digital converter in the Camshaft Position (CMP) sensor before being sent on to the Engine Control Module(ECM).

When a tooth on the pulse wheel nears the sensor the magnetic field is bent and affects the resistor located nearest to the ground, resistance affects the voltage and the output signal to the ECM is low. When the same tooth continues past the sensor the magnetic field follows and so affects the other resistor that is located nearest to the voltage supply, this resistor affects the voltage so that the output signal to the ECM is high.

The magnetic field swings backwards and forwards between the teeth on the pulse wheel and the ECM senses the signals between the teeth, partly before and partly after the sensor.

The pulse wheel has 4 teeth. The ECM calculates the time interval from one tooth to the next and can decide exactly which cylinder must be supplied with fuel and ignition spark respectively.

Faults in the CMP sensor:
- The engine can still be started and driven in event of faults in the CMP sensor.
- The engine may need to be cranked for a long time before the ECM sends a spark to the correct cylinder and the engine starts.