Crankshaft Position Sensor: Description and Operation

Information on the position and speed of the crankshaft is sent from the crankshaft position sensor to pin 49 of the electronic control module. The sensor is grounded from pin 48 of the control module.

Mounted on the crankshaft is a perforated disc with 58 ribs. The sensor, which is of inductive type, is mounted on the crankcase wall. The distance between the perforated disc and the sensor is 1.0±0.7 mm and it 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 rib 1 then passes the sensor, the control module knows that the crankshaft is 84° BTDC for cylinder No. 1.

The voltage and frequency from the crankshaft position sensor vary with engine speed. At idling speed the sensor input is 5-10 V AC, 725 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 rpm and the crankshaft position to calculate ignition timing, injection time, injection duration and idle speed control.





Fuel injection is cut off when engine speed exceeds 6,600 rpm.

As soon as the control module receives pulses 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 sensor resistance is 540±55 ohms.

NOTE: A diagnostic trouble code is always stored in the control module memory when the crankshaft is stationary. This trouble code is cleared as soon as the control module receives pulses from the crankshaft position sensor.

Engine Speed Signal
The control module sends an engine speed signal from pin 43.
This signal is a pulse train which varies between 0 and battery positive voltage with a frequency of about 37 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.