My friend, you are about the enter the dark bowels of the world of BMW.
This happened to me a month ago and I was just as upset as you are now.
Did you get a good sized income tax refund this year? If so, then get ready to spend some of it.
I attempted to fix a recurring Trans Prog by changing the fluid and filter on a 4L30E tranny with 150,000+ miles. It was happened everyother day, usually as I approached a stop. After I changed the fluid/filter, the message was on permanently.
My mechanic looked at it and called for a tranny overhaul. He said the internals were very worn. $2200 and a week later, it came back. Evidently, they forgot to clear the code stored in the ECU. Once this was done, I drove it for a week before it happened again. They changed a pressure regulator, code was coming up for that....twice.
After it happened one day later, again, they were thinking of changing the 1/2 gearing valve, since it only occured while coming to a stop. By the way, turning the car off for a few seconds did clear the message/4th gear mode.
Before doing this, they did some research and found a BMW service bulletin that described by continuing problem to a "T". The solution: a new chip ($20) for the ECU that changes the pressure sensing parameters to a more relaxed envelope. I guess the new tranny produces too much or too little pressure at times and the computer program does not like it. So, guess where my car is right now!
Should be done early this afternoon. All this extra work/labor/parts and they're not charging me a cent. I think they are taking this personally and are determined to get it fixed.
Slightly embarrassed? Maybe.
Cool enough to make it right? F'ing A right!!!!
JD