GM OEM Crankshaft Positioning Sensor, also called a knock sensor. ACDelco GM Original Equipment Engine Crankshaft Position Sensors monitor the position and rotational speed of the crankshaft, and are GM-recommended replacements for your vehicle's original components. The signal from the crankshaft position sensor is used by the engine control module to determine fuel injection and ignition timing. These original equipment engine crankshaft position sensors have been manufactured to fit your GM vehicle, providing the same performance, durability, and service life you expect from General Motors