900 SE Convertible V6-2489cc 2.5L DOHC EFI (1997)
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.
