BMW 4 Series ECU Failure: Symptoms and Solutions Alert

Hey there! I had very similar issues with my 2013 BMW 3 Series Diesel last year. Initially thought it was the ECU too, but turned out to be the main relay that was failing intermittently. Had the same symptoms, slow starts, power drops, and unusual electrical glitches. My car would sometimes take 3-4 attempts to start, and occasionally the dash lights would go crazy. Got it checked at the garage where they found the main relay was defective and starting to corrode. The mechanic showed me the old relay, contacts were pretty worn out. The fix wasn't too complex, but it was crucial to get it done quickly as it could've left me stranded anywhere. The repair involved replacing the main relay and checking the surrounding wiring harness for any damage. My car's been running perfectly since then, no more starting issues or power problems. If your symptoms match, might be worth getting the relay checked before jumping to ECU conclusions. From my experience, relay issues are more common than ECU failures in these models. Best of luck!

Thanks for sharing that info about the relay fix! You definitely described symptoms that sound exactly like what I'm experiencing. Mind if I ask how much you ended up paying for the repair? Also curious if you've had any other electrical gremlins pop up since getting it fixed? Really hoping it's just the relay in my case too and not the ECU. Would be a much cheaper fix from what I understand.

Hey again! Happy to update you! Since my last post, I actually took my car to the mechanic and you'll be glad to hear it WAS indeed just the main relay, exactly like I'd suspected in my previous reply. The whole thing cost me 120 € including labor, which was such a relief compared to what an ECU replacement would've run. And to answer your question about other electrical issues, nope, absolutely none! Everything's been running perfectly since the fix. The car starts right up every time now, no more power drops, and all those unusual electrical glitches are completely gone. It's like having a different car honestly. The mechanic confirmed what I mentioned before about these relays being a common weak point, so I'm pretty confident you're dealing with the same thing. My advice would be to get it checked ASAP though, you definitely don't want to risk getting stranded somewhere. Let us know how it turns out if you get it looked at. Always good to share these experiences so others can learn from them too!

Just wanted to update everyone! Took my car to a new mechanic yesterday and guess what, it was the relay after all! What a relief. The total bill came to about 140 in parts and labor, which feels like winning the lottery compared to what I was fearing with the ECU. Honestly, I can't believe the difference. The car starts instantly now, all the power's back, and those weird electrical issues have completely disappeared. Really glad I asked here and got that heads-up about checking the relay first. The mechanic was actually great too, showed me the old relay and explained everything clearly. Such a better experience than my last garage visit. He even mentioned these relays typically last about 5-7 years before starting to act up, so the timing makes sense for my car. Thanks again for the advice everyone, especially about the relay issue. You saved me from a lot of unnecessary stress and probably a much bigger repair bill!