Crankshaft Position Sensor: Description and Operation

Crankshaft Position (Reference) And Engine Speed Sensors:

The crankshaft position sensor (or reference sensor) is a magnetic induction type sensor located on the rear of the engine block.

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, a reference pin, located on the flywheel, passes 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. This pulse indicates the exact position of the crankshaft (60~BTDC #1 cyl.) once each revolution.

MPI Start-Up Reference Signals:

The ECU uses this information during engine cranking only, and compared with the signal from the hall sensor in the distributor, provides a reference point from which to calculate the ignition timing and synchronize the fuel injection pulses so the engine will start. Once the engine is started, the signal from the reference sensor is no longer needed, and the ECU calculates the ignition timing and fuel injection pulses using the signal from the engine speed sensor.

SELF DIAGNOSIS
A plausibility check is not necessary for this sensor, since it senses the presence of a reference pin that is permanently fixed in one position on the engine flywheel. The ECU will, however, recognize when the signal is absent, and store a fault code, indicating that the pin is missing, or there is an open or short circuit in the sensor or sensor wiring. There is no substitute signal for this sensor. If the reference sensor fails or the signal is lost (due to open or shorted wire, or missing reference pin) while the engine is running, the engine will continue to run until the ignition is turned off, but will not start again until the sensor is replaced or the sensor signal is restored (wire is repaired or reference pin is replaced).