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ABS Speed Sensor
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Alternator Current and Voltage
Amplifier Earth
Camshaft Sensor
Carbon Canister Solenoid Valve
Crankshaft sensor
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Crankshaft Sensor - Hall Effect Diagnostics

The system is used on some Vauxhall Vectra 2.0 Lt. fitted with a Simtec 56.5 engine management system. The Crank Angle Sensor (CAS) has a voltage supply which switches the output relative to the engine speed.

This system should not however be confused with the Simtec system which uses a frequency modulated signal (AC excited).

Technical Information

The Crank Angle Sensor (CAS) or Crankshaft Position Sensor (CPS) can be mounted in various locations such as: near the front pulley, to the rear of the engine into the flywheel, in the side of the engine block or within the distributor.

The output signal produced is used by the Engine Control Module (ECM) to determine the exact position of the engine.

The Hall effect type crankshaft sensor is a simple digital 'on / off' switch which produces a digital output that is recognised and processed by the ECM. The sensor is trigged by a rotating metal disc with openings, the disc passes between the electromagnet and the semiconductor.

A semiconductor has the ability to be a conductor or an insulator depending on whether the semiconductor sees, or is shielded from the magnetic field. This magnetic field is switched on and off by the rotating disc that travels adjacent to the two objects. The effect of a magnetic field that is able to pass through one of the 'windows' will stop the flow of voltage. When the 'window' is closed the flow is reinstated. This action will produce a digital square wave that is understood by the ECM or amplifier and will not need the extra Schmitt trigger circuitry to convert the analogue signal into a digital signal.



Crankshaft Sensor - Inductive Diagnostics


We can evaluate the output voltage from the Crank Angle Sensor (CAS). The voltage will differ between manufacturers, its proximity and engine speed.

The main reason for evaluating this waveform is to monitor the output when the engine stops due to a loss of High Tension voltage (HT). The waveform will be an Alternating Current (AC) its voltage will be seen to increase with engine speed.


There is a 'missing tooth' in the flywheel or reluctor and is used as a reference for the Electronic Control Module (ECM) to ascertain the engine's position. Some systems use two reference points per revolution.

Technical Information

This sensor known as a Crank Angle Sensor (CAS) or sometimes Crankshaft Position Sensor (CPS) can be mounted in various positions and can be located near the front pulley, to the rear of the engine into the flywheel, in the side of the engine block or within the distributor. The output signal produced is used by the Engine Control Module (ECM) to determine the exact position of the engine.

On an inductive CAS a resistance value should be seen between the terminals. This type of sensor is the most popular but Hall effect and AC excited sensors are also used in some engine management systems. The inductive sensor is normally a two wire device, however some manufacturers use three wires, the third being a coaxial braid to keep out any HT interference that may interrupt and corrupt the signal seen by the ECM.

The output voltage produced on this sensor will be vehicle specific and the output will reduced by any of the following three factors:

A larger air gap will decrease the voltage output from the sensor.

A failing sensor with shorted windings will also reduce the voltage output, while a sensor with an open circuit will have no output at all. The condition of the winding inside the crank angle sensor can be determined by conducting a resistance test with a multimeter.

A slower than anticipated cranking speed may also cause the output to be low; the characteristics of this being that the engine will not start when cranked, but starts if the engine is 'bump started' causing the engine to rotate faster and producing sufficient voltage to trigger the ECM. A large air gap can also give the same symptoms.


Crankshaft position sensors tend to fail as they become hot and the windings become open circuit in this instance the engine will stop but restarts if left to cool down.

Here is a typical crankshaft sensor.