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.
should not however be confused with the Simtec system which uses a frequency
modulated signal (AC excited).
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.
signal produced is used by the Engine Control Module (ECM) to determine the
exact position of the engine.
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.
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
Crankshaft Sensor - Inductive Diagnostics
evaluate the output voltage from the Crank Angle Sensor (CAS). The voltage
will differ between manufacturers, its proximity and engine speed.
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
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.
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.
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.
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.
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.
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