BMW 6 Series Diesel: Critical Transmission Warning Signs

Hey there! I have some experience working on cars, and this sounds familiar. I had a similar issue with my 2011 BMW 5 Series diesel (520d). My cousin also owns a BMW 7 Series, so I'm a bit familiar with these cars. When I had transmission troubles, it turned out to be a faulty wiring connection to the transmission control module. Had those same symptoms, warning lights, rough shifts, the whole deal. My mechanic found that some cables were damaged and had poor contact. The fix cost me 95 Euro, mostly labor for tracking down and repairing the connection issue. But before jumping to conclusions, could you share: Current mileage? Any recent transmission fluid changes? Does it happen more when the engine is cold or warm? Any other warning messages on the dash? Different BMW years and models can have varying transmission setups, so these details would help me better assist you.

Thanks for your input! My car has 136717 KM on the clock and had its last service about 3 months ago. The grinding noise is definitely worse when the engine is cold, especially in the morning. Besides the trans and engine lights, there's no other warnings showing up. Had the transmission fluid checked during service and it looked ok according to the mechanic. Your wiring issue experience is interesting, might be worth checking that out since it's a much cheaper fix than what I was fearing. Did your car also make grinding noises when you had that problem?

Hey again! Thanks for those extra details. Yes, my 5 series actually did make similar grinding noises when cold, which is partly why I thought to mention the wiring issue. It's interesting that your symptoms match up so closely with what I experienced. Just to clarify about the grinding noise, mine was most noticeable during those first few minutes of morning driving, especially when shifting between 2nd and 3rd gear. The mileage on my car was pretty similar too, around 142,000 KM when the issues started. You know what's funny? I initially thought my radiator oil pressure was the culprit too, which got me really worried about repair costs. But after the mechanic traced it to the wiring, it was such a relief. The grinding noise completely disappeared after the fix. Quick tip though, while you're getting it checked, have them look at the transmission control module connections specifically. In my case, the wires had rubbed against a nearby bracket, causing intermittent connection issues. These BMWs are known for having occasional electrical gremlins. Let me know what you find out. Given how similar our issues sound, I'm really curious if it turns out to be the same problem. Would be a much better outcome than a major transmission repair!

Thanks so much for the detailed response! This is super helpful and giving me some hope. Yes, that's exactly when I hear the grinding, between 2nd and 3rd gear during cold starts! Can't believe how similar our issues are. The fact that your repair was so affordable is making me feel much better about this whole situation. I've just called my mechanic and scheduled a check-up for tomorrow morning. Specifically asked them to inspect the wiring and transmission control module connections, mentioning your experience with the rubbed wires. Really hoping it turns out to be something this straightforward rather than a major transmission overhaul. Will definitely update once I know what's wrong. Really appreciate you taking the time to share your experience. It's given me a solid lead to investigate and saved me from panicking about potential massive repair bills!