BMW 5-Series Trans Failure: TCU Issues & Grinding Gears

Hey there! I had some experience with similar transmission issues on my 2011 BMW 3 Series (coming from someone with some experience working on cars). The symptoms were almost identical to what you're describing. After dealing with rough shifts and limp mode, I took it to my regular workshop. Turned out the transmission control unit was indeed faulty. The repair set me back about 1000 Euro, but it solved the problem completely. The grinding sounds disappeared and the paddle shifters started working perfectly again. What's your exact engine variant and mileage? This info would help me share more specific details about what to look out for, as different variants can have slightly different issues. Also, has your transmission fluid been changed recently? Let me know and I'll try to provide more targeted advice.

Thanks for sharing your experience! I've got the gasoline variant with 33555 KM on the clock, and just had my latest service done. Your repair cost sounds about right based on what I've been quoted. Good to hear it fixed the issue completely. The transmission fluid change is actually a good point, I'll definitely have that checked when I take it in. Did you notice any warning lights on the dash before the problems got worse?

Hey again! Yes, actually I did notice warning lights before things got worse on my 3 Series. First, it was just an occasional transmission warning light that would come and go, but I initially ignored it (big mistake!). After about a week, the check engine light joined in, and that's when the transmission started acting really weird. Looking back at my situation, and seeing you've got relatively low mileage, I'd strongly recommend getting it checked sooner rather than later. When mine started showing these symptoms, I waited too long hoping it would sort itself out, and that just made everything more stressful. The grinding noise especially got worse over time. Since you mentioned you just had a service done, did these issues start before or after? In my case, the problems began about a month after a routine service, which made me wonder if something got disturbed during maintenance. The fluid check is definitely crucial, my mechanic found that even though the level was fine, the fluid quality wasn't great. The good news is that once the control unit was replaced, it was like having a new car again. Just make sure you go to someone who really knows BMWs, I learned that lesson the hard way after a general mechanic misdiagnosed it first time around.

Really appreciate the detailed response about your experience! The issues actually started about two weeks after my service, which is pretty similar to your timeline, that's quite interesting. I've got both warning lights now too, so hearing about your experience has convinced me not to wait any longer. You're absolutely right about the specialist thing, I've already booked it in with a BMW-certified workshop for next week rather than trying my luck with a general mechanic. The grinding noise has definitely been getting worse over the past few days, so I'm glad I'm not delaying it further. I'll make sure to specifically ask them about the fluid quality too, not just the levels. It's actually really reassuring to hear that the control unit replacement made such a difference to your car. Thanks for taking the time to share all this, it's helped me feel much more confident about what I'm dealing with!