Speed Sensor
Speed sensor is attached to drive plate housing. This sensor detects the flywheel drive plate teeth as they pass during engine operation and provides engine speed and crankshaft angle information to the ECU. See Fig 1 .
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 and notch pass the magnet core in the sensor, the concentration and then collapse of the magnetic field 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 the magnet core in the sensor, the increased concentration and then collapse of the magnetic field induces a higher voltage (spike) into the sensor pick-up coil winding. The higher voltage (spike) indicates to the ECU that a piston will be at the TDC position 12 teeth later. The ignition timing for the cylinder is either advanced or retarded as necessary by the ECU according to the sensor inputs.