BMW iX3 Won't Start: ECU Power Supply Mystery Solved

Hey there! I have some experience with EVs and had a similar issue with my 2019 BMW i4 (also own an iX). The symptoms you're describing sound exactly like what I faced. After taking it to the workshop, they found a loose connection in the main control unit's wiring harness. The cable connections had deteriorated, causing intermittent power supply issues. The repair was pretty straightforward, they replaced the faulty connectors and secured the wiring properly. Cost me around 95 Euro and it's been working perfectly since then. Before going to the workshop, I tried basic troubleshooting like checking the 12V battery voltage and fuses, but with these modern EVs, it's usually best to let the pros handle electrical issues. Can you share more details about when this started happening? Does it happen out of nowhere or under specific conditions? This info would help determine if you're dealing with the same problem I had.

Thanks for sharing your experience! Mine is also intermittent, happens out of nowhere and definitely sounds similar to what you experienced. I've had my iX3 since 2021 (17822 KM on the clock) and this is the first major electrical issue I've faced. I also checked the 12V battery and fuses as a first step, but no luck there. Will probably take it to the workshop this week. Just wanted to gather some insights before heading in, so your repair info is really helpful. Good to know it could be something as "simple" as a wiring harness issue rather than a more complex system failure.

Hey again! Thanks for the additional details about your iX3. Yeah, the symptoms are identical to what I experienced, the unusual nature of the issue is particularly telling. With my i4, it started exactly the same way at around 19000 KM, so we're in the same ballpark mileage-wise. Since your basic checks didn't reveal anything (just like in my case), I'm even more convinced it's the same wiring harness problem. When they fixed mine, the technician mentioned these issues are more common in EVs than people think because of all the complex electronics and the vibrations affecting the connections over time. Quick tip: when you take it to the workshop, make sure to mention the intermittent nature of the problem. In my case, this helped them narrow down the diagnosis faster. They might want to keep your car for a day to properly test everything, but it's worth it for the peace of mind. Let me know how it goes after the workshop visit. Always curious to hear if these similar cases end up having the same root cause. These EVs are fantastic cars, but they definitely have their quirks!

Really appreciate your detailed follow-up! The similarity between our cases is quite striking, especially with the mileage and intermittent issues. That's super helpful to know about mentioning the unusual nature of the problem to the techs, will definitely do that. I've already called the workshop and booked it in for tomorrow morning. They said they might need to keep it for 24-48 hours, which makes sense given what you mentioned about thorough testing. It's actually quite reassuring to hear these issues are somewhat common in EVs, was worried I had a lemon! Just hope it's the wiring harness like in your case and nothing more serious. I love this car otherwise, and you're right about EVs having their quirks. Will definitely keep an eye on any vibration-related issues going forward too. Thanks again for all your help and insights!