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Camshaft Position Sensor

This sensor can also be referred to as the Cylinder Identification (CID) sensor. As the engine rotates the sensor will signal to the Electronic Control Module (ECM) that cylinder number one is approaching Top Dead Center (TDC) and the timing of the injection pulse can be determined. On an inductive sensor, a resistance value should be seen between its terminals with these terminating back at ECM. The output signal from these units can be in either analogue or digital format (sine wave or square wave) and will depend on the manufacturer concerned. Vaxuhall have also used a Alternating Current (AC) excited sensor on their Simtec engine management system, which is described later in this section.

It is unlikely that a failed camshaft position sensor will cause the engine not to start, as this particular sensor only times the injector pulses. When this sensor is disconnected the point at which the injector fires can be seen to 'shift' giving an incorrect point at which the fuel is delivered behind the inlet valve.

Fig. 34.1

Figure 34.1 shows a typical camshaft position sensor.

Vauxhall ECO TEC - AC Excited Camshaft Sensor

This camshaft sensor differs in operation from the other sensors by having an Alternating Current (AC) voltage supply to the CID sensor. The ECM supplies a very high frequency at around 150 Khz (2500 cycles per second) to an exciter coil that is located in close proximity to a rotating disc.
The disc is located at the end of the camshaft and has a section removed that when 'open' allows the frequency to excite the receptor (through mutual inductance) and returns the signal to the ECM, indicating the position of number 1 cylinder.