The digital motor electronics (DME) engine management systems in BMW E83 X3 vehicles with an M54 engine use the engine control module (ECM) to control fuel injection, ignition and other important drivetrain functions. The ECM sequentially triggers the fuel injectors to spray fuel into the intake ports and then, a split-second later, triggers the ignition coils to fire the spark plugs. This sequence of events is timed by using the crankshaft position. Using the signal from the crankshaft sensor, the ECM "knows" which cylinder is ready for fuel intake and then, later, for ignition.
The crankshaft position sensor is located near the starter motor, mounted in the engine block. The sensor reads a toothed reluctor wheel mounted to the end of the crankshaft. It then sends a signal to the DME used to identify cylinder location. If this signal is missing, for example from a faulty crankshaft sensor, then the engine will not start. You can consider the signal from the crankshaft sensor the RPM signal for the DME.
In this article, I'll go over the steps involved with replacing the crankshaft position sensor. Access from below is difficult due to the front driveshaft and tight fit of the suspension and engine. I suggest removing the throttle housing and replacing it from above.
Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.
Vehicle models change and evolve as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.
Remove the throttle body. See our tech article on throttle body removing.
The crankshaft sensor (green arrow) is located below the starter motor (yellow arrow) at the left side of the engine.
Once the Allen bolt is removed, pull the crankshaft out of the engine block. Be sure that the sealing O-ring comes out with the sensor. If it stays in the block, retrieve it with a small pick (yellow arrow). Install the new sensor and sealing O-ring. Torque the sensor to the crankcase. Reconnect the electrical connector and install the vacuum reservoir, throttle body and remaining parts. Start the vehicle and allow it to idle for about one minute. Check that the crankshaft sensor area is free of oil leaks. If your check engine light was on, now is the time to clear any fault codes, and you are done.