BMW i5 High-Voltage Failure: What's Behind Power Loss?

I have some experience working on EVs. Had a similar issue with my 2022 BMW i4 (also considered the iX before buying). Last year, my car showed the same symptoms, power reduction followed by system shutdown. Turned out the high-voltage battery was severely discharged due to a faulty cell. My trusted workshop diagnosed it, replaced the defective module, and recalibrated the battery management system. Cost me around 290 Euro total, but it was worth fixing it properly. Could you share more details about: How long have you owned the car? What's the current mileage? Did you notice any warning signs before this happened? Can you share the exact error code? This info would help better understand if you're dealing with the same issue I had. BMW's electric systems are quite similar across models, so my experience might be relevant to your case.

Thanks for sharing your experience! I've had the car since it was new, and I'm at 100717 KM. Unfortunately, I didn't note down the error code before the system went completely dark. The only warning sign I noticed was that the range estimate seemed a bit off for about a week before this happened, showing inconsistent numbers even with similar driving conditions. I'll definitely get those error codes for you once the workshop pulls them tomorrow. Just had my latest service about three weeks ago, and everything seemed fine then. Really hoping it's not as serious as your battery cell issue!

Hey again! Thanks for providing those details. Based on what you're describing, especially the inconsistent range estimates before the shutdown, it does sound quite similar to what I experienced with my i4. Those range fluctuations were actually one of the first signs I noticed too, though I didn't connect the dots at the time. Since you mentioned your recent service was just three weeks ago, this is pretty unexpected. My issue started showing up around 95,000 KM, so we're in a similar ballpark mileage-wise. The good news is that if it is a faulty cell like in my case, it's a fairly straightforward fix, though it does take a few days. Quick tip: when you get the error codes tomorrow, make sure they check the individual cell voltages in the battery pack. In my case, one cell was showing significantly lower voltage than the others, which was causing the whole system to act up. Have you noticed any other quirks lately? Like slower charging speeds or the battery draining faster than usual? These were some other symptoms I experienced but didn't pay much attention to initially. Also, did the car shut down while you were driving or when it was parked?

Thanks so much for the detailed follow-up! Actually, now that you mention it, I did notice the charging was taking longer than usual at my last few charges, but I just chalked it up to the colder weather. The shutdown happened while I was stopped at a traffic light, thankfully not while I was moving at speed. I'll definitely ask them to check those cell voltages tomorrow, that's really helpful advice. This makes me feel a bit better about the whole situation, knowing it might be similar to what you experienced. I was worried it might be something more major or complicated. I'll update you tomorrow once I get the diagnostic results and error codes from the workshop. Thanks again for sharing your experience, it's super helpful to have some idea of what I might be dealing with!