BMW 8 Series Won't Start in Park, Transmission Nightmare

I had a similar issue with my 2019 BMW M850i last summer. The symptoms matched yours exactly, car only starting in gear, check engine light, and jerky transmission shifts. Took it to the garage and they diagnosed it as a faulty transmission control module. The main control unit was defective and needed replacement. The repair wasn't a quick fix, they had to order the part and reprogram the new module to sync with the car's systems. The car was in the shop for about 4 days. It was definitely a serious issue that needed immediate attention because it could've led to complete transmission failure. Since the fix, my car has been running perfectly, no more rough shifts or starting issues. You should get this checked soon at a certified dealer or reputable BMW specialist. The transmission control unit isn't something you want to risk with an inexperienced mechanic. Looking at your symptoms, it sounds exactly like what I dealt with. Hope this helps with your decision.

Thanks for sharing your experience, that's really helpful as it sounds exactly like my problem. Just wondering, do you remember roughly how much the whole repair set you back? Also, has everything stayed running smoothly since the fix, or have you noticed any other quirks pop up? Trying to get a sense of whether this might be a one-and-done fix or if I should be prepared for more issues down the road.

Hey again! Happy to fill you in on the details. The repair cost me 1000 € to fix the faulty control unit, and I can honestly say it was worth every penny. Since getting it sorted at the mechanic, my M850i has been running like a dream, the parking position works perfectly now, and all those annoying transmission issues are completely gone. No more problems starting the car, and the shifting is buttery smooth again. The best part? I haven't had a single problem since the repair was done. No weird quirks, no warning lights, nothing. It really was a one-and-done fix for me. Just make sure you get it looked at by someone who knows what they're doing with BMWs, it makes all the difference. Once they replace and program that control unit correctly, you should be good to go. Trust me, getting it fixed properly the first time around will save you headaches later. My car feels just like new again, and I couldn't be happier with how it turned out.

Thanks for all that detail, really puts my mind at ease! You convinced me to bite the bullet and get it checked out. Actually just got back from a certified BMW specialist yesterday. Turns out it was exactly what you described, faulty transmission control module. The repair cost was pretty close to what you paid too, around 1100 €. They had my car for three days, but wow, what a difference! Took it for a test drive today and it's running perfectly, starts smoothly in park, no more check engine light, and the transmission shifts like butter now. Should've done this sooner instead of worrying about it. Really appreciate you sharing your experience, helped me make the right call on getting it fixed at a proper shop. Nice to know I shouldn't have any more issues with it. Time to enjoy driving my 8 Series again without stressing about every gear shift!