1993 325i - I have an auto transmission that slips into "limp mode"(stuck in 3rd gear) shortly after running. Intially the pressure regulator was replaced with no inprovement or change in symptoms. The transmission was then replaced with a used unit which subsequently had the same problem.
I discussed with the independent mechanic that it sounds more like a logic issue than mechanical one so he replaced the main CPU with a borowed one from a known good car and the problem remains with the transmission. Therfore, he replaced the transmission a third time and it too has the same problem (each time this occurs I am charged with 10hrs labor - $4,000 to this point).
The independent mechanic and local BMW dealer insist the problem is truly a defective transmission and the only solution is to be able to eventually find one without the problem. Because the transmissions otherwise operate flawlessly, my belief is that BMW unknowingly assembled these cars with a defective transmission sending unit which misinterprets a pressure, fluid level or temperature and sends an incorrect code.
In an effort to solve this problem myself and stop the bleeding, I believe that if I can identify which wire these signals are transmitted on I can override the error with an appropriate high/low voltage or ground. In other words, I believe the symptoms are being misdiagnosed. Thoughts?