BMW Z3 Trans Won't Start in Park, Shifting Issues

Hi there! I have some experience working on BMWs. Had a similar issue with my 2002 BMW Z4 last year, and my cousin owns a 3-series. That sounds really familiar actually. My Z4 had almost identical symptoms, trouble starting, rough shifting, and warning lights. Turned out the transmission control unit was fried. Had to take it to a specialist workshop where they diagnosed and replaced the unit. The whole thing cost me about 1000 Euro, but the car's been shifting perfectly since then. Before you proceed though, what's your current mileage and have you checked the transmission fluid level? Also, could you share the specific error codes you're getting? This would help narrow down if you're dealing with the same issue I had. Feel free to share more details, and I'll try my best to help based on my experience.

Thanks for sharing your experience! My Z3 has 66927 KM on the clock and just had its service last month. The symptoms do sound similar to what you described. I've noted down the error codes and will check the transmission fluid level tomorrow. Really appreciate the tip about the transmission control unit, that's definitely something I hadn't considered. The repair cost you mentioned seems reasonable compared to what I was expecting. Has anyone else dealt with transmission control unit issues on these older BMW models? Would love to hear more experiences before I take it to a specialist.

Hey again! Thanks for following up about your Z3. Yeah, those TCU issues are more common than you'd think on these models. After I had mine fixed, I actually ran into another Z4 owner at my specialist workshop who had the exact same problem. His mileage was pretty close to yours too, around 70K. From what I understand, these transmission control units can start acting up regardless of mileage, it's more about age and electronic degradation. The good news is that since your car just had a service last month, you can probably rule out a lot of the basic stuff. Just make sure to check that transmission fluid though, I learned the hard way that even a slightly low level can cause weird behavior. Quick tip from my experience: when you take it to the specialist, ask them to check the wiring harness connected to the TCU as well. In my case, they found some corroded connections that needed cleaning. Saved me from potential future issues. Keep us posted on what you find out with those error codes. If they're anything like what I had, we might be able to confirm if it's definitely the TCU before you spend money on diagnostics.

Really appreciate all the detailed advice! The point about checking the wiring harness is super helpful, definitely something I'll mention to the specialist. It's reassuring to hear about similar cases with successful repairs. Just checked the error codes: P0706 and P0750, which after googling seem pretty consistent with TCU issues. I'll be taking it to a specialist workshop next week. The transmission fluid check will have to wait until tomorrow when it's light out, but I'll definitely do that first. Thanks again for sharing your experience, it's given me a much clearer idea of what I'm dealing with. I'll update this thread once I get it sorted in case anyone else runs into similar problems with their Z3 or other BMW models.