BMW i8 ECU Power Issues, Terminal 15 Investigation

Hey there! I have some experience working on hybrid vehicles. I actually faced a similar issue with my 2017 BMW i3. The symptoms were nearly identical, no engine crank and ECU power problems. Took it to my regular workshop and turns out it was a loose connection in the wiring harness connecting to the ECU. They had to trace the cables, found a damaged connector, and replaced the affected wiring section. Total repair cost was 95 Euro and it's been running perfectly since then. Before jumping to conclusions though, could you share: Does the issue happen consistently or intermittently? Are you getting any specific error codes? Have you noticed any warning lights before this started? This might help narrow down if you're dealing with the same problem I had. From my limited electrical knowledge with these BMWs, the Terminal 15 connection could definitely be the culprit, but it's best to get a proper diagnosis.

Thanks for sharing your i3 experience! For my i8 (117208 KM), it's happening intermittently, usually when the car sits unused for 2-3 days. Getting error code P0562 consistently, and the battery warning light flickers occasionally before the starting issue occurs. Had it serviced last month but they didn't catch this problem. Really frustrating as it's been super reliable until now. Think I'll need to get it checked specifically for the wiring harness based on your experience.

Hey again! Thanks for those extra details about your i8. That flickering battery light and the P0562 code definitely ring some bells, it's very similar to what I experienced with my i3 before getting the wiring sorted. The intermittent nature after sitting for a few days is interesting, that's exactly how mine started acting up too. Since you mentioned the recent service, I'd bet they might have accidentally disturbed some connections while doing other work. That's actually what caused my issue, turned out some wiring got slightly displaced during a routine maintenance check. Quick tip from my experience, when you take it in, ask them to specifically check the ground connections too, not just the positive terminal. In my case, they initially focused only on the positive side, but the real culprit was actually a corroded ground connection that was causing the intermittent power loss to the ECU. The good news is that if it's similar to what I dealt with, it's typically not a major repair. Mind keeping us posted on what they find? Always curious to learn more about these quirky electrical gremlins in our hybrids!

Thanks so much for the detailed follow-up! You've given me more confidence about what to look for. I'll definitely get the workshop to check both the ground connections and wiring harness thoroughly. The similarity between our issues, especially the intermittent nature and behavior after sitting idle, makes a lot of sense. Just got off the phone and booked it in for next week, specifically mentioning the points you raised. I made sure to tell them about checking those connections that might have been disturbed during the last service. Really appreciate you sharing your experience, it's helped me feel less worried about what could've been a much bigger problem. I'll update the thread once I get it sorted!