I have a 2001 525i and the check engine light goes on and off constantly. It may stay on for a couple of days and then it goes off for two or three days. My husband has one of those testers to find out what the problem is and it showed the crankshaft position sensor is defective. Does anyone know what that is and where it is located? Is it possible for my husband to repair it himself or do we need to take it to a BMW Service Center? This problem is causing the car to go dead on occasions. Especially when I stop at a light or stop sign. I really would like to get this problem solved because I dont want to cause something else to go wrong because of this one thing.

Please Help!