BMW Z3 ECU Power Mystery: No Voltage & Won't Start

I had a similar issue with my 2005 BMW Z4 last month. The ECU voltage problem turned out to be a damaged wiring harness near the firewall connector. The insulation had worn out causing intermittent connection issues. The mechanic found several corroded pins in the main ECU plug, plus a failing ignition switch that wasn't sending proper signals. It wasn't a quick fix, they had to replace the wiring harness section and the ignition switch assembly. This was definitely a serious electrical issue that needed immediate attention to prevent potential ECU damage. The repair took two days because they had to trace the entire circuit to make sure there weren't any other compromised sections. Better to fix it properly than risk further electrical problems down the line. In my case, the car's been running perfectly since the repair. If you're getting zero voltage to the ECU, I'd definitely have a professional check the wiring harness and ignition switch first. These components often fail around the mileage you're describing.

Thanks for sharing your experience! Glad to hear they found the root cause with the wiring harness and got your Z4 running properly again. My symptoms sound pretty much identical to what you described. Quick question, do you remember roughly how much the whole repair set you back? Also, has everything been running smoothly since then, or have you noticed any other electrical quirks popping up? Just trying to get an idea of what I might be in for with this repair.

Hey there! Just wanted to follow up on your question about the repair costs. After I wrote about my Z4's issues, I actually took it back to the mechanic because the "Terminal 15 ignition positive interrupted" warning kept coming up. They found it was just a loose cable connection, much simpler than we initially thought! Only cost me 95 € to fix the connection, which was such a relief after worrying it might be something major. And to answer your question, since they fixed that connection, everything's been running perfectly. No more electrical gremlins or warning messages. The car starts right up every time now. It's amazing how something as simple as a faulty connection can cause so much trouble, right? Way better outcome than the complex wiring harness issue I originally suspected. I got really lucky that it turned out to be such a straightforward fix. Sometimes with these electrical issues, you're preparing for the worst, but it ends up being something relatively minor. Hope your repair turns out to be similarly straightforward!

Thanks for the update about your car! I actually just got back from the mechanic today. Turns out my situation was different than initially feared. The mechanic found a blown fuse and a failing relay that were causing the ECU voltage issues. Much cheaper fix than I expected, parts and labor came to around 200. The repair only took a few hours, and the car's running great now. Started right up when I turned the key! Such a relief after stressing about potentially major electrical problems. Definitely learned my lesson about jumping to worst-case scenarios. I'll keep an eye out for that Terminal 15 warning you mentioned, just in case. But for now, I'm just happy to have my Z3 back on the road without breaking the bank. Really appreciate you sharing your experience, it helped me stay calm while dealing with this whole situation!