BMW 7-Series: ECU Issues Causing Multiple System Failures?

Hey there! I had a similar issue with my 2008 BMW 5-series diesel (had the 530d). I've got some experience working on cars, but mostly basic maintenance stuff. This sounds exactly like what happened to me last year. Initially thought it was the ECU too, but turned out to be just a faulty main relay. The symptoms were identical, sluggish start, weak engine response, and electrical systems going crazy. Took it to my regular workshop, they diagnosed and replaced the main relay. Cost me about 120 Euro total, and the car's been running perfectly since. Much cheaper than an ECU replacement! Before I can share more specific details though, could you tell me which engine variant you've got in your 7-series? Also, are you getting any specific error codes? This would help me determine if it's the same issue I faced. If it is the same problem, it's actually a pretty straightforward fix. My mechanic had it sorted in about an hour.

Thanks for your reply! I've got the M57 engine in mine, and yes, getting error codes related to voltage fluctuations. Just checked my service history, last maintenance was at 98387 KM and everything was working fine until last week. What's interesting is my symptoms do match yours, especially the unusual electrical gremlins and poor engine response. Did your relay issues also cause the engine to occasionally hesitate during acceleration? That's another thing I'm experiencing. The relay fix sounds promising and definitely better for my wallet than an ECU replacement. Did you notice any warning signs before it completely acted up? Would really appreciate any additional details about the symptoms you faced.

Hey again! Yeah, absolutely, I had the same M57 engine in my 530d, and what you're describing with the hesitation during acceleration is exactly what I experienced! It was super frustrating, especially when trying to merge onto highways. Before it got really bad, I noticed some small signs for about 2-3 weeks, occasional flickering of the dashboard lights and sometimes the car would take a split second longer to start in the mornings. I actually ignored these at first (big mistake!) until one day the problems just snowballed. The voltage fluctuation codes you're getting are another match with my situation. My mechanic explained that when the main relay starts failing, it causes inconsistent power delivery to various systems. That's why you're getting those unusual electrical issues and the engine performance problems, it's all connected. You know what's really interesting? After the relay replacement, I realized the car had been gradually losing its punch for weeks, but it happened so slowly I didn't notice until I got it fixed. The difference after the repair was like night and day! Given how similar your symptoms are to what I experienced, I'd bet good money it's the same issue. Just make sure your mechanic checks the relay connections too, mine had some slight corrosion that needed cleaning. Let me know how it goes if you get it checked out. Always happy to help a fellow BMW owner!

Thanks so much for all this detailed info! Your experience is super helpful, especially since we've got the same engine. You've actually made me feel a lot better about this whole situation, was dreading a massive repair bill for the ECU. What you mentioned about the gradual power loss is really eye-opening. Now that I think about it, my car has probably been losing performance gradually too, but I just didn't pick up on it. And those early warning signs you described, the flickering dash lights and delayed starts, I definitely had those but didn't think much of it at the time. I've just called my mechanic and scheduled an appointment for tomorrow. Mentioned the relay issue to him, and he agreed it's worth checking first before jumping to more expensive solutions. He's also going to look at those connections you mentioned for corrosion. Really appreciate you taking the time to share your experience in such detail. Will definitely update you once I get it sorted. Thanks again for helping me potentially save a bunch of money and stress!