BMW X4 Transmission Nightmare: Multiple System Failures

Hey there! I have some experience working on BMWs and had a similar issue with my 2016 X3 last year. The symptoms you're describing sound exactly like what I went through, my X3 started acting up with jerky shifts and those annoying grinding noises. The M40i was also known for these problems. I took it to my workshop, and after diagnostics, they found a faulty transmission control unit. They had to replace it completely, set me back about 1000 Euro, but it fixed all the issues. The car's been shifting smoothly ever since. Before I can give you more specific advice, could you share: Current mileage on your X4? Are there any other warning lights on the dash? Did these issues start suddenly or develop gradually? This will help me understand if you're dealing with the same problem I had. Transmission issues can be tricky, and it's better to get them sorted quickly before they cause more damage.

Thanks for the detailed reply! Mine's at 132465 KM and had its last service about 3 months ago. The warning lights started appearing gradually over the past two weeks, with the transmission light being the most recent one. The shifts became noticeably worse after that. I'm a bit worried since I've heard these repairs can get pretty expensive. Good to know about your experience with the control unit, at least that gives me a starting point when I talk to the mechanic. Mine does sound eerily similar to what you went through.

Hey again! Thanks for providing those details about your X4. Yeah, that mileage is pretty close to when my issues started too, I was around 140,000 KM when my transmission started acting up. From what you're describing, it's even more likely that you're facing the same TCU issue I had. The gradual deterioration of the shifting quality followed by the warning light is exactly how mine played out. The fact that it started after a recent service is interesting though, mine also began showing symptoms shortly after routine maintenance. I'll be honest, the repair wasn't cheap, but it was worth every penny to get the car shifting properly again. My mechanic mentioned that these TCUs can sometimes get damaged from voltage fluctuations or just wear out over time. One thing I learned from my experience, don't wait too long to get it fixed. I drove mine for about a week after the warning light came on, and the grinding got worse. Could have caused more damage if I'd kept pushing it. Quick tip: have them check the wiring harness too while they're at it. My mechanic did a full inspection and found some minor corrosion in the connectors. Getting those cleaned up as part of the repair probably helped prevent future issues. Let me know how it goes after you get it checked out. Always curious to hear if others have the same fix work for them.

Thanks so much for all this information, it's really helpful! I'll definitely get it checked out this week and won't risk driving it much until then. The tip about the wiring harness is great, I'll make sure to mention that to the mechanic. It's actually a relief to hear someone else had the same issue and got it sorted, even though the cost isn't something I'm looking forward to. I suspect you're right about the TCU, especially since our mileage is so similar. I'll update this thread once I get the diagnosis and repair done, might help others with similar issues in the future. Really appreciate you taking the time to share your experience!