BMW Z3 Auto Trans Failure: Diagnosing Limp Mode Issues

Hi there! I'm somewhat experienced with BMWs and had a similar issue with my 2002 BMW Z4 last year (also had a Z8 before). The symptoms you described sound really familiar. My car was also stuck in limp mode and shifting terribly. Turned out it was an undervoltage problem affecting the transmission control module. Had my trusted mechanic check it out, and after running diagnostics, they found the voltage wasn't reaching the proper levels. Fixed it for about 240 Euro and it's been running smoothly since. Could you share more details about when exactly this started happening? Also, when was the last time you had your transmission fluid changed? This could help pinpoint if we're dealing with the same issue. Let me know these details and I might be able to offer more specific advice from my experience.

Thanks for sharing your experience! My Z3 has 35610 KM on the clock and just had its service last month, but the transmission fluid wasn't changed then. The issue started about a week ago, first with slight hesitation during shifts, then progressively got worse until the warning light came on. Interesting that you mention the voltage issue, would explain why it sometimes seems better in the morning when the battery's fully charged. Will definitely have the mechanic check the voltage levels when I take it in. Thanks for pointing me in this direction!

Hey again! Yeah, what you're describing definitely strengthens my voltage theory. My Z4 showed the exact same pattern, smoother operation after sitting overnight with a fully charged battery. Had almost identical mileage too when this happened (around 37000 KM). The morning vs rest-of-day difference was what helped my mechanic diagnose it quickly. Since the transmission control module is pretty sensitive to voltage fluctuations, even a slight drop can trigger these symptoms. Just a heads up though, while my issue was voltage-related, it'd still be smart to get that transmission fluid changed since you mentioned it wasn't done in the recent service. My mechanic always says these BMWs really benefit from fresh transmission fluid every 50000 KM or so, regardless of what the manual states. I'd love to hear what your mechanic finds. Keep us posted! If it turns out to be the same voltage issue, the fix should be pretty straightforward and not too expensive. Hope this helps narrow things down for you.

Thanks so much for the detailed follow-up! You're really helping me feel more confident about this situation. I've actually just booked an appointment with my mechanic for tomorrow morning, and I'll definitely have them check both the voltage and the transmission fluid. Makes total sense about the fluid change interval too, definitely overdue for that. I think between your experience and the similar symptoms, we're probably looking at the same issue. Really appreciate you taking the time to explain everything, especially about the voltage sensitivity of these transmission modules. I'll make sure to post an update once I get it sorted out. Thanks again for sharing your knowledge, it's exactly the kind of firsthand experience I was hoping to find!