Speed Sensor

The speed sensor (or crankshaft position sensor) is mounted at the flywheel/drive plate housing. The sensor detects the flywheel/- drive plate teeth as they pass during engine operation and sends an electrical signal to the ECU, which calculates engine speed.

The flywheel/drive plate has a large trigger tooth and notch located 90° and 12 small teeth before each top dead center (TDC) position. When a small tooth or notch pass the magnetic core in the sensor, the build-up and collapse of the magnetic field induces a small voltage signal in the sensor pick-up windings.

The ECU counts these signals representing the number of teeth as they pass the sensor. When a larger trigger tooth and notch pass the magnetic core, a higher voltage signal is sent to the ECU. This indicates to the ECU that a piston will be at the TDC position 12 teeth later. The ECU either advances or retards ignition timing as necessary according to sensor inputs.