BMW X3 ECU No Power: Terminal 15 Circuit Problem?

Hi there! I had a similar issue with my 2011 BMW X5 last year, and I've got some experience working on cars (though I'm no expert). When mine wouldn't start, I was also getting ECU voltage errors. Took it to my regular workshop, and it turned out to be a faulty wiring connection between the ignition switch and the ECU. The cable had worn out over time, causing an intermittent connection. The repair, including labor and parts, cost me around 95 Euro. Could you share some more details about your X3? Like, does it make any clicking sounds when you try to start it? Are you getting any other warning lights on the dash? Also, when did this start happening, was it sudden or gradual? This info would help me understand if you're dealing with the same problem I had. Really hope this helps point you in the right direction. The X3 is pretty similar to my old X5 in terms of electronics, so it might be the same issue.

Thanks for sharing your experience! Mine is in pretty good shape (last serviced about 2 months ago at 74330 KM), but this problem came out of nowhere yesterday. Actually, I do hear a faint clicking sound when turning the key, and the dash lights flicker briefly before going completely dark. No other warning lights before this happened, was working perfectly fine until I parked it after work. I'm a bit relieved to hear your repair wasn't too complicated. Did you try any troubleshooting before taking it to the workshop? I'm somewhat handy with basic car maintenance, but electrical issues always make me nervous. Wondering if I should attempt to check the connections myself or just take it straight to a mechanic.

Hey again! Good to hear back from you. Yeah, those symptoms sound exactly like what I experienced with my X5. That clicking and flickering you mentioned, that's pretty much a carbon copy of what mine was doing. Before taking it to the workshop, I actually did try some basic troubleshooting. First checked the battery connections, they were fine. Then I tried to trace the wiring from the ignition switch, but honestly, these BMWs are pretty complex when it comes to electronics. I spent about an hour poking around with a multimeter before realizing I was in over my head. What I learned from my experience is that while it's tempting to DIY, the diagnostic equipment these cars need for electrical issues is pretty sophisticated. My attempt at fixing it myself could have potentially made things worse, especially since everything's so tightly packed in there. Since you mentioned you're handy with basic maintenance, you could check the obvious stuff like battery terminals and fuses, but I'd honestly recommend getting it to a pro for this particular issue. The wiring harness might need proper testing, and that's not something you can really do without the right tools. Quick tip though, document everything you're experiencing (the clicking, flickering, etc.) before taking it in. Really helped speed up the diagnosis in my case.

Thanks for the detailed response. After considering your advice, I think I'll play it safe and take it to a professional. I just checked the battery terminals and fuses as you suggested, all look clean and properly connected, but the problem persists. You're right about these electrical issues being tricky, and I'd hate to make things worse by poking around too much. What really convinced me is what you said about the diagnostic equipment. My basic multimeter probably won't cut it for tracking down an ECU-related problem. Plus, if it is indeed similar to your wiring issue, I'd rather have someone with proper tools and experience handle it. I've already written down all the symptoms and when they started, just like you recommended. Hopefully, this will help speed up the diagnosis process. I'll schedule an appointment with my regular BMW specialist tomorrow morning. Thanks again for sharing your experience, it's really helped me make a more informed decision about how to handle this!