Crank Position Sensors

From M-Tech Automotive

The crank sensor, sometimes called a VR, or Variable reluctance sensor, is used to monitor the position or rotational speed of the crankshaft. This information is used by our [engine management systems] to control ignition system timing and other engine parameters.

Crank sensors in engines usually consist of magnets and an inductive coil, or they may be based on magnetically triggered Hall effect semiconductor devices. Common mounting locations include the main crank pulley, the flywheel (as in Fords), and occasionally on the crankshaft itself (such as the Vauxhall Red-top engine). This sensor is the most important sensor, in that if it is not functioning correctly you will lack an RPM signal to the ECU, halting all ECU operations including injection and ignition.

It typically consists of 2 or 3 connections. (2 being the most common as used on Ford Engines, and indeed is the prefered sensor type) with GM vehicles sometimes using 3-pinned connectors. In both cases 2 wires are the signal wires, and in the case of the 3-pin plug, the 3rd is the shield.