BMW X3 Won't Start Properly, Trans Issues & Check Engine

Hey there! I had a similar issue with my 2011 BMW X5 (also had a BMW 3 Series before). I've got some experience working on cars, but nothing too advanced. My symptoms were almost identical, rough shifting, check engine light, and starting problems. After trying a few local shops, I found a good mechanic who diagnosed it as a faulty transmission control unit (TCU). The repair cost me around 1000 Euro, including parts and labor. The shop replaced the TCU and reprogrammed it, fixed the problem completely. Haven't had any issues since then. Could you share your exact error codes? Also, how many miles/kilometers are on your X3? This info would help determine if you're dealing with the same problem I had.

Thanks for sharing your experience! Mine has 117024 KM and just had its service last month. The symptoms do sound quite similar to what you experienced. My mechanic initially thought it might be the TCU too, but we haven't confirmed it yet. The repair cost you mentioned is actually less than I expected, which is somewhat relieving. Did you notice any warning signs before the problem fully developed? My transmission was actually shifting fine until last week when it suddenly started acting up.

Hey again! Thanks for the follow-up. Yeah, I absolutely remember the progression of my TCU issues. Actually, just like your case, my transmission was working perfectly fine until it suddenly started acting weird. Looking back, I did notice some very subtle signs maybe a week before it went bad, there was this tiny delay when shifting from park to drive, but it was so minor I didn't think much of it at the time. Your mileage is pretty close to what mine was when I had the issue (mine was around 125,000 KM). And since you mentioned having a recent service, I doubt it's maintenance-related. Sounds more and more like we had the same TCU problem. Quick tip from my experience, when my mechanic replaced the TCU, he suggested getting the transmission fluid checked and possibly changed too. I did that as a preventive measure, and I think it helped ensure everything worked smoothly afterward. Also, while 1000 Euro might sound okay, remember prices can vary depending on where you get it fixed. Independent shops specializing in BMW usually charge less than dealerships, and the quality of work can be just as good. My previous 3 Series actually had similar issues, and the dealership quoted me almost double what I ended up paying at my trusted mechanic. Let me know how it goes with your X3. I'm curious to hear if it turns out to be the same issue!

Thanks so much for all the detailed information! Your experience is really helpful, especially the tip about the transmission fluid check. I'll definitely mention that to my mechanic. It's actually quite reassuring to hear that someone else had such similar symptoms, and that it was fixable without breaking the bank. I've already called a few independent BMW specialists in the area, and you're right, their quotes are way more reasonable than the dealership's initial estimate. I'm planning to take it to a highly-rated independent shop tomorrow morning. They mentioned they've dealt with lots of TCU issues on BMWs, so fingers crossed they can sort it out quickly. I'll probably skip the dealership altogether based on what you've shared about the price difference. It's great to know I can get quality work done for less. Thanks again for all your help, it's made me feel much more confident about getting this fixed!