BMW M3 Radiator Fan Failure & Overheating Issues Solved

Hey there! I've got some experience with cars. Had a similar issue with my 2017 BMW M4 last summer. The symptoms were exactly like yours, overheating, lazy fan, and that annoying check engine light. Turned out the speed sensor was acting up, which was messing with the fan control system. Took it to my regular workshop, and they diagnosed it pretty quickly. The faulty sensor wasn't sending the right signals to the fan control module. The fix wasn't too complicated, but they had to replace the sensor entirely. Set me back about 250 Euro, but it's been running perfectly since then. Before I can share more specific advice, could you share: Have you noticed any other warning lights? Does this happen more when idling or while driving? Have you checked your coolant level? These details would help me understand if you're facing the exact same issue I had.

Thanks for sharing your experience! My car just hit 88115 KM and had its latest service about 3 months ago. I've noticed this happens mostly when idling, and coolant levels look fine. No other warning lights except the check engine one. Been keeping an eye on the temperature gauge like a hawk. Good to know about that speed sensor issue, definitely sounds similar to what I'm experiencing. I'll get it checked out asap since these cooling problems can get serious pretty quick. Hopefully it's just the sensor like in your case and nothing more complex.

Hey again! Yeah, after reading your response, I'm even more convinced it's similar to what I experienced with my M4. The fact that it's happening mostly at idle is a really familiar pattern, that's exactly how mine acted up. And like yours, my coolant levels were fine too. Since your service was just 3 months ago, I'm betting they would've caught any major cooling system issues then. In my case, I actually drove around for about a week before getting it fixed (probably not the smartest move, looking back), and the symptoms were super consistent with what you're describing. Just to share a bit more from my experience, after they replaced that speed sensor, they also did a full diagnostic scan just to be safe. Might be worth asking your mechanic to do the same. Mine found that the fan control module was actually fine, it was just getting wonky signals from that bad sensor. The price I mentioned earlier ended up being pretty standard from what I've heard from other BMW owners. And honestly, it was worth every penny to get it sorted properly. Been about 8 months now since the fix, and my cooling system's been working like a charm. Let me know how it goes when you get it checked out, curious to see if it's the same issue!

Thanks so much for all the detailed info! Really helpful to hear about your experience, especially since our situations sound so similar. I've already called my mechanic and booked it in for tomorrow morning, definitely not taking any chances with the cooling system. Your advice about getting a full diagnostic scan makes total sense. I'll make sure to ask for that too, just to be thorough. Honestly, if it ends up being just the speed sensor like yours, I'll be relieved. The 250-euro price tag sounds way better than what I was imagining, was worried it might be something major with the cooling system. I'll keep you posted on what they find. Thanks again for taking the time to share your experience, really helped put my mind at ease!