BMW 3 Series Hybrid Transmission Nightmare: Help Needed

Hi there! I have some experience working on cars and faced something very similar with my 2011 BMW ActiveHybrid 5. Those symptoms sound really familiar. Had the same issues, erratic shifting, grinding, warning lights. Initially thought it was just the display too. Took it to my trusted workshop and it turned out the transmission control unit was failing. They diagnosed it through their computer system and confirmed the TCU was the culprit. The fix wasn't cheap, set me back about 1000 Euro for the new control unit and programming, but it solved all the problems. I also own a BMW 7 Series and these electronic gremlins can be tricky in these cars. Could you share more details about your specific error codes? Also, when exactly does the grinding occur, during shifts or at specific speeds? This would help narrow down if you're dealing with the same issue I had. Hope this helps! Let me know if you need more info.

Thanks for sharing your experience! That does sound similar to what I'm experiencing. In my case (153087 KM), the grinding noise happens mainly during upshifts, especially between 2nd and 3rd gear. The error codes I'm getting are P0705 and P0750, both transmission-related. Just had my service last month and everything else was fine, so it's definitely isolated to the transmission. Did your mechanic mention anything about the transmission fluid when they replaced the TCU? Just wondering if I should get that checked while they're at it. Hoping I can get away with a simpler fix, but after reading your post, I'm mentally preparing for that TCU replacement cost!

Hey again! Thanks for those additional details about your BMW. You know what's crazy? Those are exactly the same error codes I got with my ActiveHybrid 5! And yeah, the grinding between 2nd and 3rd was my nightmare too. Actually, when they were replacing my TCU, they did check the transmission fluid and I'm glad they did. Found out it was a bit low and had some metal particles in it. They recommended a fluid change along with the TCU replacement. I went ahead with it since they were already working on the transmission, figured might as well do everything at once, you know? The fluid change added about 300 Euro to my bill, but honestly, it was worth it. The shifts became butter-smooth after that. My mechanic mentioned that low or degraded fluid can actually contribute to TCU problems, so it makes sense to check both. Just a heads up though, if your mileage is around 153K, definitely get that fluid checked. Mine was at 140K when this happened, pretty similar to yours. The transmission fluid condition might give you more insight into what's really going on in there. I know it's not the news you wanted to hear about potentially needing a TCU, but at least you'll be going in prepared. Keep me posted on what you find out!

Thanks so much for the detailed follow-up! It's actually reassuring to hear someone went through the exact same thing with the same error codes. I'll definitely take your advice about the transmission fluid check, makes total sense to do everything while they're in there. Just booked an appointment with my mechanic for next week. Going to show them your comments about the TCU and fluid situation. At least now I know what I'm potentially dealing with and can budget accordingly. Really appreciate you taking the time to share all this info and the heads up about the costs. Guess I'll have to bite the bullet and get it sorted properly rather than trying any quick fixes. Will probably go for both the TCU replacement and fluid change if needed, better to do it all at once like you did. Thanks again for all your help!