Crankshaft Position Sensor

PRINCIPLE OF OPERATION, CRANKSHAFT POSITION SENSOR






Crankshaft position sensor--supplies the control module with information on the position and speed of the crankshaft via pin 41.

A perforated disc with 58 ribs is mounted on the crankshaft. The sensor is of inductive type and mounted in the crankcase wall of the engine. The distance between the sensor and the perforated disc is within the range of 0.4-1.3 mm. This distance is not adjustable.

The sensor acts as a generator and supplies a sinusoidal alternating current. The control module can determine engine speed by measuring the frequency of this current. Two ribs are missing after the 58th rib on the perforated disc. When rib 1 passes the sensor, the control module knows that the crankshaft is 117° before top dead centre (BTDC).

The voltage from the crankshaft position sensor varies with engine speed. At idling speed it is 7-10 V (AC) and at 2500 rpm about 15-20 V (AC). However, it is the frequency and not the voltage which is of interest to the control module.

The control module mainly uses engine speed and the crankshaft position to calculate ignition timing, fuel injection timing, fuel injection duration, boost pressure and idle speed control.

Fuel injection is turned off when engine speed exceeds 6200 rpm on cars with a turbo engine and 6500 rpm on cars with a normally aspirated engine.

As soon as pulses from the crankshaft position sensor are received by the control module, it grounds the main and fuel pump relays.

If the sensor does not work or if there is a break in the circuit, the engine will not start.

The resistance of the sensor is 540 ±55 ohms.





Engine Speed Signal
The control module emits an engine speed signal from pin 58.

The signal is a pulse train which varies between 0 V and battery positive, measuring about 28 Hz at idling speed and about 85 Hz at 2500 rpm. This corresponds to 2 pulses per crankshaft revolution.

The engine speed signal is used by the tachometer and the electronic throttle system (ETS).


Cars with ETS
If the engine speed signal is shorted to ground, the engine can be started but will stop shortly afterwards.