A crank sensor is used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters.
The crank sensor is used to «synchronize» a four stroke engine upon starting, allowing the management system to determine when to inject the fuel.
It is also used in combination with a similar camshaft position sensor to monitor the relationship between the positions of the pistons and valves in the engine, which is particularly important in engines with variable valve timing.
This sensor, among others functions, is commonly used as the primary source for the measurement of engine speed in revolutions per minute.