Engine Speed Sensor: Description and Operation

Crankshaft Position (Reference) And Engine Speed Sensors:

The engine speed sensor located on the rear of the engine block, is a magnetic induction type sensor.

Crankshaft Position Sensor And Engine Speed Sensor:

The sensor 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.

MPI Start-Up Reference Signals:

The engine speed sensor signal is also used to calculate the position of the crankshaft at any given time. The flywheel has 135 teeth around its circumference. Each tooth generates a pulse when it passes the speed sensor, representing 2.6° of crankshaft rotation. Once TDC for the #1 cylinder is established (by the crankshaft position reference sensor), the ECU counts the number of flywheel teeth that pass the sensor, and continuously calculates the position of the crankshaft, to determine ignition and injection timing for each cylinder.


SELF DIAGNOSIS
The ECU will recognize the absence of a signal and store a fault code, indicating an open or shorted sensor or sensor circuit. There is no plausibility check for this input, however, the ECU uses this signal, along with the signal from the air mass sensor, to check the plausibility of the idle switch signal. There is no substitute signal for this sensor. If the engine speed sensor fails or the signal is lost due to a wiring problem (open or shorted wire), the engine will not start or run. If the sensor signal is corrupt or intermittent, the engine may or may not start, but will run very poorly if it does start.