BMW X3 Power Loss & System Failures: ECU Problems?

Hey there! I've got some experience working on BMWs and had a similar issue with my 2020 BMW X1. The symptoms you're describing sound exactly like what I went through. In my case, it turned out to be a faulty main relay, not the ECU itself. When I took it to my trusted workshop, they diagnosed it pretty quickly. The repair was straightforward and cost me about 120 Euro. Since then, everything's been running smoothly, no more unusual shutoffs or sluggish performance. Before jumping to conclusions about the ECU, could you share: Does this happen only on cold starts? Which fault codes are you getting? Have you noticed any warning lights? This info would help me compare it more accurately with my experience. BMWs often share similar electrical components across models, so it might be the same issue.

Thanks for sharing that info about the relay! I've got 186628 KM on my X3, and just had it serviced last month. I'm actually getting these issues regardless of cold or warm starts. The main warning lights that keep popping up are for the stability control and engine management. The most frequent fault code I'm getting is P0685, along with some communication errors between modules. Your relay suggestion is really interesting, definitely sounds less scary than a full ECU replacement. Did you notice any specific patterns before your relay completely failed? I'm thinking of taking it to the shop next week, but wanted to gather some more insights from fellow BMW owners first.

Hey again! Thanks for providing those details, and wow, those symptoms do sound really familiar! When my X1 had the relay issue, I actually got very similar fault codes, including that P0685. Before my relay completely failed, I noticed the problems would come and go out of nowhere, just like you're experiencing. The stability control and engine management lights were definitely my constant companions too! Mine would sometimes clear up after restarting the car, but would always come back, super annoying, right? What really caught my attention in your reply is the communication errors between modules, that's exactly what my car was showing. With my relay problem, it was basically disrupting the power supply to various control modules, which explains all those communication errors. Just to add to my previous repair experience, before I got it fixed, I tried resetting the codes a couple times, but they kept coming back within a day or two. The workshop showed me the old relay afterwards, and you could actually see some burn marks on the contacts. I'd definitely suggest getting it checked out sooner rather than later. While my repair was relatively simple, driving with these symptoms isn't great for other components. Keep me posted on what your workshop finds, I'm really curious if it turns out to be the same issue!

Thanks so much for all that detailed information! It's really reassuring to hear your experience was so similar, especially those communication errors and the way the problems kept coming back after clearing the codes. I've actually noticed the same pattern with the restart temporarily fixing things. I just called the workshop and scheduled an appointment for next week. Made sure to mention the relay issue you experienced and the P0685 code, they seemed pretty interested in that info. Keeping my fingers crossed it's just the relay and not the full ECU. You're right about getting it checked soon, I don't want to risk damaging other components. I'll definitely update this thread once I get it diagnosed and fixed. Really appreciate you taking the time to share your experience, it's helped me feel much more informed about what might be going on with my X3!