Crankshaft Position/Engine Speed Sensor

This sensor detects drive plate teeth as they pass by during engine operation. This sensor provides ECU with engine speed and crankshaft angle position.

The drive plate has 3 large trigger notches 120 degrees apart. There are 20 small teeth between each trigger notch. Each large trigger notch is located 12 small teeth before each Top Dead Center (TDC) of the corresponding pistons.

When a small tooth and notch pass under the magnet in the sensor, the concentration and then collapse of magnetic flux induces a small voltage spike into the sensor pick-up coil winding. These small voltage spikes enable the ECU to count the teeth as they pass the sensor.

When a large trigger tooth and notch pass under the sensor, there is a longer than usual delay between voltage spikes. The longer delay tells the ECU that a piston will be at TDC position 12 teeth later. The ECU can advance or retard ignition timing as necessary, according to sensor inputs.