Crank sensor is a component used in an internal combustion engine to monitor the crankshaft position or rotational speed. Crank sensor data is used by ECU engine management systems to control ignition system timing and other engine parameters. The crank sensor can be used in combination with a similar camshaft position sensor to monitor the relationship between the pistons and valves in the engine, which is particularly important in engines with variable valve timing. It is also commonly the primary source for the measurement of engine speed in revolutions per minute.

Crankshaft position sensor also known as the crank position sensor is an electronic device used in an engine to record the rate at which the crankshaft is spinning. This information is used by the ECU to control ignition and fuel injection. The sensor system consists of a rotating part, typically a disc, as well as a static part, the actual sensor. The functional objective for the crankshaft position sensor is to determine the position and rotational speed (RPM) of the crank.

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, and occasionally on the crankshaft itself. This sensor is the most important sensor in modern day engines. When it fails, there is a small chance the engine will start (engine will likely cut out after a few minutes of driving) but it mostly will not start.

Some engines, such as GM’s Premium V family, use crank position sensors which read a reluctor ring integral to the harmonic balancer. This is a much more accurate method of determining the position of the crankshaft, and allows the computer to determine within a few degrees the exact position of the crankshaft (and thereby all connected components) at any given time. Another type of crank sensor is used on bicycles to monitor the position of the crankset, usually for the cadence readout of a cyclocomputer.

A bad crank position sensor can worsen the way the engine idles, the pistons fire, or the acceleration behaviour. If the engine is revved up with a bad or faulty sensor, it may cause misfiring, motor vibration or backfires. Accelerating might be hesitant, and abnormal shaking during engine idle might occur. In the worst case the car may not start.