Speed Sensor
Speed sensor is secured by special shouldered bolts to flywheel/drive plate housing. Speed sensor is nonadjustable and preset at factory. Speed sensor senses TDC and engine speed by detecting flywheel teeth as they pass pick-up coil during engine operation. See Fig 1 .
Flywheel has a large trigger tooth and notch located 12 small teeth before each TDC position. When a small tooth and notch pass the magnetic core in sensor, concentration and collapse of the magnetic field created induces a small voltage spike into sensor pick-up coil windings. These small voltage spikes are sent to ECU, allowing ECU to count the teeth as they pass sensor.
When a large tooth and notch pass magnetic core in sensor, increased concentration and collapse of the magnetic field induces a higher voltage spike than smaller teeth. Higher spike indicates to ECU that a piston will soon be at TDC position, 12 teeth later. Ignition timing for cylinder is either advanced or retarded by ECU based upon "sensor input".