I took my X3 to BMW dealer for fuel gauge problem (jump up and down.) The dealer changed the sensor with a full tank of fuel as courtesy. However, the car ran out of gas on me when the gauge was still showing Quarter tank full. I doubt if the sensor unit is the cause of problem. Can someone tell me what other parts involve that can go wrong and some steps to narrow the source of problem? Is there a service manual for this car or X5 in general?