The speed sensor is an electromagnetic sensor that is able to detect the crankshaft rotational speed and the crankshaft position. It is usually installed at the outer rim of the flywheel of the crankshaft.  The gathered data will be transmitted to the engine management system to calculate ideal fuel ignition- and fuel injection times.

In case of a defective crankshaft sensor the engine management system will issue a diagnostic trouble code and ignite the check engine light. If the crankshaft sensor does not work properly the driver might experience an unstable engine running and even starting problems.

The cause of failure can be pollution, corrosion, broken cables or a broken crankshaft sensor wheel.