Crankshaft Position Sensor: Description and Operation

Distributor Exploded View:

Crank Angle And #1 TDC Sensor:

SENSOR OPERATION
The crankshaft angle sensor and the No.1 cylinder TDC sensor are composed of a disc and optical module assembly. The disc contains 360 slits around its circumference to indicate the crankshaft angle. An additional six light-transmission slits located 60° apart located inward from the edge are used to indicate each cylinder's top dead center position.

The pick-up module assembly uses two luminous diodes and two photo diodes to detect the two different slits. The disc rotates within a slight clearance between the luminous diodes and the photo diodes.

As the distributor shaft rotates, the slits at the disc's edge pass between the light and the optical reading part of the module. The light emitted from the luminous diodes passes through the slits to the photo sensing diodes.

When the photo diodes receive the light, they become conductive and generate a signal, which is sent to the Control Module.

CRANKSHAFT ANGLE SIGNAL:
Top dead center is detected by the signal obtained from the outer series of slits (1° slits) by reading the 10° blank spot. The ECM, based upon this signal, determines which of the six pulses from the TDC sensor is the signal for the No. 6 cylinder (reference cylinder), thus synchronizing the ECM with the rotation of the disc in the distributor. This allows the ECM to determine (with the use of its preset firing order) which pulse is the No.1 cylinder.

The outer circumference slits are also used by the ECM to assist in a more accurate ignition timing at engine speeds below 1200 rpm. The Control Module is able to detect number one cylinder TDC by the comparing the signal generated through the inner slits on the disc and the blank space on the outer slits and calculating the position.



No.1 CYLINDER TDC SIGNAL:
The six slits located at the inner circumference of the disc serve to detect the position of the pistons relative to top dead center. The ECM, based on this signal, determines the fuel injection timing, and also calculates the amount of intake-air, the timing of the ignition signal, etc. for each revolution of the engine.