The crank sensor is either located on the main crank pulley, the flywheel, the camshaft or on the crankshaft itself. The most common location is at the bottom of the engine block, where the crankshaft is.
The crank sensor is one of the most important sensors in a car, if not the most important. Without the crank sensor or if the sensor itself is faulty, a car might not start or it might have issues while running, like cutting out. This sensor is the one that is going to feed the electronic control unit with a signal that measures the engine's revolutions per minute. Without the crank sensor feeding the RPM signal, the electronic control unit is not able to control the ignition system timing properly.
Common issues regarding a faulty crank sensor are misfiring, backfire, engine experiencing an irregular idle, the acceleration behavior becomes irregular, the engine won't start after heating up but has no problems starting once it cools down again. Most common causes of a crank position sensor failure are by exposure to extreme heat. This problem has been solved with more recent car models because the latest crank sensors are now closed units, which prevents damage from extreme heat, water or other fluids.