The crankshaft position sensor records how fast the crankshaft is spinning. This speed is then used by the car's internal computer for proper fuel injection and ignition. There are actually two parts to the sensor: a disc that rotates and the sensor which remains in place. The most typical type of sensor works off of the Hall Effect which uses a magnet. Many of the failure symptoms are similar to issues that other parts will have when they fail, so often times it can take several tries to uncover whether it is sensor that is the problem.
1 - Check Engine Light
This can be frustrating as the check engine light can obviously turn on for many different things. Your mechanic will need to hook up to your car's internal computer to determine that it is the sensor failing. Many times this light may go off when the car is running, but when you start the car again after it has been off for a while, the light has turned off. This occurs when the sensor stops working due to high heat levels. Once the vehicle cools down it will function again.
2 - Cylinder Misfiring
Only one of the cylinders needs to misfire to cause a problem. Many times misfiring is due to issues with the spark plug, but if the sensor fails then the computer is not getting the correct information on crankshaft position. Many people will not check the sensor, but if you have fixed everything else and there are still problems, checking it should be next on the list.
3 - Acceleration Hesitation
This is also similar to the cylinder misfiring. If there is some type of hesitation in acceleration, then the computer is not getting the correct information on the position of the crankshaft when the car is running. There is a lag between the computer receiving data from the crankshaft position sensor and applying it, so it takes the car that little bit of time to accelerate.
4 - Intermittent Starting
This is the most serious of the symptoms that could occur. When the sensor completely fails then the internal computer will have a malfunction code. If the car continues to have difficulty starting and you do not have it fixed, then one day it will not start at all. Many times this type of failure is because there is a problem with the electrical connection. There may be a problem with the circuit. If the signal to the computer begins to fail then this can cause the spark plugs to fail and eventually shut off the engine.
5 - Engine Vibrations
Once the sensor fails then the position is not monitored, so you may find that the engine starts to have very strong vibrations. This will in turn affect the engine power and running properly.
6 - Backfiring and Stalling
Your car may stall from time to time. It can stall a few seconds after starting or quite some time after starting, and the same goes for backfiring. You will also notice that the car keeps backfiring frequently, not just every so often.
7 - Irregular Car Function
Basically you will notice that regular engine workings will start to become irregular, such as speed fluctuations, irregular acceleration, idling fluctuations, and more. If you start to notice a lot of odd and irregular workings then have your crankshaft position sensor checked.