Engine Speed Sensor: Description and Operation

Reference Mark And Engine Speed Sensor:

The engine speed sensor located on the rear of the engine block, is a magnetic induction type sensor. It contains a permanent magnet, and an iron core surrounded by an induction coil. The magnet sets up a magnetic field around the iron core. As the engine turns, the teeth of the flywheel pass in close proximity to the end of the iron core, disturbing the magnetic field. This change in the magnetic field induces a small current in the coil surrounding the iron core, creating a wave-like pulse that the ECU can detect. The frequency of this pulse indicates the speed of the engine. The ECU counts the number of pulses per unit of time and calculates the rpm of the engine. This information is also compared to information from other sensors to determine engine load and establish points on ignition and fuel enrichment "maps" which are permanently stored in the ECU's memory.