The crank position sensor, sometimes referred to as the crankshaft position sensor, is a small plug found on motor vehicles that monitors the speed at which the crankshaft is rotating. This information is relayed through the vehicle’s computer, which then uses it to calculate ignition timing. Crankshaft sensors may go bad because of faulty construction or high mileage on the vehicle.
If a crankshaft position sensor goes bad, no signal will be transmitted to the PCM (Powertrain Control Module, or the car’s computer), which will result in a failure to start. The crankshaft position sensor can be checked by a mechanic with a special tool that will test the sensor to see if it is responsible for the problem.
If the crank position sensor is going bad but still functional at times, the vehicle may start normally but then fail to start on a different occasion. In some cases, the vehicle may start and run fine, but then shut down without warning while driving.
If the crankshaft position sensor is going bad, the “Check engine” light may come on. Depending on the vehicle, a faulty crank position sensor could also result in error codes near the tachometer when the key is turned to the “On” position three times.