what does the crankshaft sensor do

The crankshaft sensor, also known as the crankshaft position sensor (CKP), is an electronic device used in internal combustion engines to monitor the position or rotational speed of the crankshaft. It is one of the two most important sensors in modern-day engines, together with the camshaft position sensor. The crankshaft sensor can be used in combination with a similar camshaft position sensor (CMP) to monitor the relationship between the pistons and valves in the engine, which is particularly important in engines with variable valve timing. The crankshaft position sensor is positioned so that teeth on the reluctor ring attached to the crankshaft pass close to the sensor tip. The reluctor ring has one or more teeth missing to provide the engine computer (PCM) with the reference point to the crankshaft position. The sensor measures the rotation speed (RPMs) and the precise position of the engine crankshaft. The crankshaft position sensor is used to set ignition timing, detect engine RPM and relative engine speed, and synchronize the fuel injector and coil firing sequence. Without a crankshaft position sensor, the engine wouldnt start. A faulty crankshaft sensor can cause an engine not to start or cut out while running. Symptoms of a bad or failing crankshaft position sensor include an illuminated Check Engine Light, uneven acceleration, rough idling, and reduced gas mileage.