The purpose of this test is to evaluate the correct operation of an inductive camshaft sensor based on the output voltage and frequency with the engine at idle speed.
Plug a BNC test lead into Channel A on the PicoScope, place a black clip on the test lead with the black moulding (negative) and a Back-pinning Probe on the test lead with the coloured moulding (positive). Probe each of the two connections until the larger waveform is displayed, the smaller waveform being the earth return.
Alternatively the TA012 two-pin test lead adapter can be used, as illustrated in Figure 1.
The camshaft sensor is sometimes referred to as the Cylinder Identification (CID) sensor or phase sensor and is used as a reference by the Electronic Control Module (ECM) to time the sequential fuel injection.
This type of sensor generates its own signal and therefore does not require a voltage supply to power it. It is recognisable by its two electrical connections, with the occasional addition of a coaxial shielding wire.
The voltage produced by the camshaft sensor is determined by several factors: the engine speed, the proximity of the metal rotor to the pick-up and the strength of the magnetic field produced by the sensor. The ECM needs to see the signal when the engine is started for its reference; if this is absent it can alter the time at which the fuel is injected. The driver may not be aware that the vehicle has a problem if the CID sensor fails, as the drivability may not be affected.
The characteristic of a good inductive camshaft sensor waveform is a sinewave that increases in magnitude as the engine speed is increased and usually provides one signal per 720 of crankshaft rotation (360 of camshaft rotation). The voltage will be approximately 0.5 volts peak to peak while the engine is cranking, rising to around 2.5 volts peak to peak at idle as seen in the example.
This sensor can also be referred to as the Cylinder Identification (CID) sensor. As the engine rotates the sensor signals to the Electronic Control Module (ECM) that the engine is approaching number 1, allowing the ECM to determine the timing of the injection pulse. On an inductive sensor, a resistance should be seen between its terminals, with these terminating back at the 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. GM/Vauxhall/Opel have also used a Alternating Current (AC)-excited sensor on their Simtec engine management system.
It is unlikely that a failed camshaft position sensor will cause the engine not to start, as this sensor only times the injector pulses. When the sensor is disconnected, the angle at which the injector fires can be seen to 'shift' causing the fuel to be delivered behind the inlet valve at the wrong time.
Figure 2 shows a typical camshaft position sensor.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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