OBDII code P0336 / Crankshaft position sensor A circuit range/performance.

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Hi, OBDII code P0336 / Crankshaft position sensor A circuit range/performance. Sometimes two times in a day, sometimes once in two days, my engine stalls while the car is running and power engine light is on. Then, I start the car immediately without any problem and it's running like it did before. i recently changed the spark plugs, but it doesn't help. What could be the problem? If it's the sensor problem, where is the location in order to change the same one. Thank you in advance, Zoran