I thought it was the reverse switch on my 1998 328i 5pd stick. I bought new BMW reverse switch and put on tranny underneath. Didn't help. It kept blowing fuses (10 amp in mine) - the fuse box (on mine anyway) is the box by the master cylinder under hood.
I took car to local independant garage (good cheap dudes that used to be GM and Ford techs - and have BMW expereince) and they found a main power harness was pinched and had a screw going into it from a factory wire harness clip under the engine, and the wires were bare and burnt away. They spliced in new wire and fixed the clip and everything is good as new. They said it never looked as if anyone had messed with it before (the area under the engine) so it must have been some factory error during assembly - although they said that is unusual for BMW. They had a heck of a time finding it since it was in a tight area near the rear of the eninge, they fouind it by following the smoke from the shorted wire!
I never got an OBC message, and CHECK CONTROL always said ok, - I just noticed that my reverse lights quit working. Maybe that helps you some.