Crankshaft Position Sensor: Description and Operation

Information on the position and speed of the crankshaft is sent from the crankshaft position sensor to pin 78 of the electronic control module. The sensor is grounded via pin 20 of the control module.

Mounted on the crankshaft is a slotted ring with 58 ribs. Of inductive type, the sensor is mounted on the wall of the engine crankcase. The distance between the slotted ring and the sensor is 1.0 ±0.7 mm. This distance is not adjustable.

The sensor acts as a small alternator and generates a sine-wave AC voltage. By measuring the frequency of this current, the control module can determine engine rpm.

Two ribs are missing after the 58th rib. When the first rib passes the sensor, the control module knows that the crankshaft is 84° before top dead centre (BTDC) for cylinder No. 1.

The voltage and frequency signals from the crankshaft position sensor vary with engine speed. At idling speed the sensor input is 5-10 V AC, 775 Hz, and at 2500 rpm it is 15-20 V AC, 2400 Hz. The frequency is of interest to the control module since it is directly proportional to engine speed.

The control module mainly uses engine speed and the crankshaft position as a basis for calculating ignition timing, injection time, injection duration and for idle speed control.





Fuel injection is cut off when engine speed exceeds 6440 rpm.

As soon as the control module receives signals from the crankshaft position sensor it grounds the fuel pump relay, causing it to operate.

Should the sensor fail to work or in the event of a break in the circuit (no continuity), the engine will not start.

The resistance of the sensor is 860 ±90 Ohm.

Engine Speed Signal.
The control module sends out an engine speed signal on pin 80.

This signal is a pulse train which varies between 0 V and battery positive voltage (B+) with a frequency of about 40 Hz at idling speed and about 125 Hz at 2500 rpm. This corresponds to three pulses per crankshaft revolution.

The engine speed signal is used by the main instrument display panel, the TCS and the transmission control module (TCM).