Camshaft position sensor - Hall effect

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

How to perform the test

Plug a BNC test lead into Channel A on the PicoScope. Place a large black clip on the black (negative) plug and a Back-pinning Probe on the colored (positive) plug. Probe each of the three connections: the sensor's voltage supply, a ground and the Hall effect output. The Hall effect output has been monitored in the example waveform shown on this page.

Figure 1 shows the fly lead multiplug for the Hall effect camshaft sensor being probed on a GM/Vauxhall/Opel ECOTEC engine.

The timebase may need to be altered if the signal is checked at varying engine speeds.

Example waveform (5 V)

Example waveform (12 V)

Waveform notes

The camshaft sensor is sometimes referred to as the Cylinder Identification (CID) sensor and is used as a reference to time the sequential fuel injection. The signal waveform can be either a permanent magnetic sine wave or in this case a digital square wave.

The Electronic Control Module (ECM) needs to see the signal when the engine is started for its reference; if this is absent, it can put the ECM into 'limp-home'.

The characteristic of a good Hall effect waveform is clean, sharp switching. As with all Hall units, it has three electrical connections.

Technical information

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 and the timing of the injection pulse can be determined. On an inductive sensor, a resistance value should be seen between its terminals that terminate back at the ECM. The output signal from these units can be in either analogue or digital format (sine wave or square wave) depending on the manufacturer. GM/Vauxhall/Opel 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 prevent the engine from starting, as this sensor only times the injector pulses. When this sensor is disconnected, the injector timing shifts, causing the fuel to be delivered at the wrong time behind the inlet valve.


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.

Suitable accessories

  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • PicoScope Battery Clip


  • Large Dolphin/Gator Clips


  • Premium Test Lead: BNC to 4 mm, 3 m


  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)


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Guided test: Camshaft sensor - hall effect