BMW M3 Trans Issues: Park Lock Causing Multiple Problems?

Hey there! I've got some experience with cars (moderate expertise level). Had a similar issue with my 2010 BMW M5 last year. The symptoms you're describing sound very familiar, my car had the exact same problems with rough shifting and check engine light. Turned out the transmission control unit was faulty. Had it diagnosed at my regular workshop, and they found the control unit was completely dead. The repair set me back about 1000 Euro, but it solved all the issues, no more rough shifts or warning lights since then. Before I can provide more specific advice, can you tell me: Have you had any transmission fluid leaks? What error codes are you getting? Did you notice any metallic sounds during shifts? By the way, if you're considering fixing this yourself, I'd strongly advise against it. The control unit programming requires specific diagnostic tools. A BMW specialist workshop would be your best bet. Let me know those details, and I'll try to help further!

Thanks for the detailed response! You're right, my M3 is showing similar symptoms. Just had my latest service done two weeks ago, and the shop said transmission fluid levels were fine. Currently at 120874 KM, and this is my first major transmission issue. The error codes I'm getting are P0700 and P0715. Haven't noticed any metallic sounds during shifts, but there's definitely a noticeable lag between gear changes. It's getting worse when the engine is cold. Your experience with the control unit issue seems pretty close to what I'm dealing with. Did your shop have to reprogram the unit, or was it a complete replacement? Just trying to get a rough idea of what I'm in for. Thanks for offering to help!

Hey again! Thanks for the follow-up. Yeah, those error codes on your M3 are exactly what I encountered with my M5! P0700 is definitely transmission control system related, and P0715 typically points to the input/turbine speed sensor circuit. Given that your fluid levels are good, this strengthens my initial suspicion about the control unit. In my case, they had to do a complete replacement of the control unit. Reprogramming wasn't an option because the unit was totally fried. The cold weather performance issues you're mentioning? Had the exact same thing, it was especially bad during morning starts. After they installed the new unit, they had to program it to match the car's specifications. The whole process took about two days because they had to order the part. But honestly, it was worth the wait. The transmission's been shifting like butter ever since. One tip though, if you decide to get it fixed, make sure they check the wiring harness connected to the control unit too. In my case, there was some minor corrosion on the connectors that they cleaned up during the repair. Might save you from future headaches. Keep me posted on what you decide to do. Happy to share more details about my repair experience if you need them!

Thanks so much for all this detailed info! It's really helpful to hear from someone who's been through the same thing. Actually feeling a bit relieved now knowing there's a clear solution, even though it'll cost a bit. I've already called my regular BMW specialist and booked it in for next week. Mentioned the control unit and those error codes to them, and they seemed to agree with your diagnosis. They're going to do a full diagnostic check first, but said they'll definitely look at the wiring harness too, great tip on that! Really appreciate you taking the time to share your experience. Having some real-world context makes this whole situation less stressful. Will probably need to dip into my savings a bit, but better than risking more damage to the transmission. Thanks again for all your help! Actually feeling pretty confident about getting this sorted now.