BMW M3 Knock Sensor Issues? Common Symptoms Explained

Hey there! I had very similar issues with my 2016 M4 last month. Started with the same symptoms, check engine light, poor acceleration, and terrible fuel economy. Everyone kept pointing to the knock sensor, but when I finally got it diagnosed, it turned out to be just a loose connector on the mass airflow sensor. The mechanic showed me how the cable connection had worked itself loose over time, causing erratic readings. They cleaned the sensor contacts, secured the connection properly, and reset the system. The fix wasn't complex, but it definitely needed proper diagnosis since these symptoms can point to various issues. Had to park the car for three days though, parts department needed to verify if we needed a replacement connector, but thankfully we didn't. Not a serious issue in the end, but those symptoms sure made it feel like one. Don't just assume it's the knock sensor, get it properly scanned first. These symptoms can be misleading. Just my two cents from dealing with something similar.

Hey! I'm really glad you shared this! I went through almost exactly the same thing with my M3 about 6 months back. My mechanic also first suspected the knock sensor, but it turned out to be the MAF sensor too. Really curious, do you remember roughly how much you ended up paying for the fix? Also, has everything been running smoothly since then? I'm asking because I've noticed some weird vibrations lately and wondering if it might be related.

Hey again! Just wanted to follow up, while I initially thought my issue was similar to yours, I actually did end up having the knock sensor problem after all! The MAF sensor symptoms were really similar, but the vibrations you mentioned made me get it checked again. Turned out the knock sensor was definitely acting up. Got it fixed last week, they found a damaged cable connection to the knock sensor that needed sorting out. Cost me 95€ to fix, which wasn't too bad considering how much better the car runs now. No more weird vibrations, engine's running smooth as butter, and fuel consumption is back to normal. The car feels like new again, honestly wish I'd gotten it properly diagnosed sooner instead of assuming it was the MAF sensor. My M4's been running perfectly since the repair, no problems at all. If you're still getting those vibrations, definitely get them checked out, better safe than sorry with these performance cars! Let me know how it goes if you get it looked at. Always good to share experiences with these things.

Thanks for getting back to me! I actually just got back from the mechanic today and thought I'd update you all. Finally got the issue sorted, turned out you were spot on about the knock sensor! They found some damaged wiring that was causing the sensor to send weird signals to the computer. Getting to this point was quite a journey though. Had to try three different shops before finding someone who really knew what they were doing. The first two kept pushing for expensive repairs I didn't need. But this new guy was fantastic, showed me exactly what was wrong and explained everything super clearly. The repair took about four hours, but the difference is incredible. No more check engine light, acceleration is crisp again, and the car's not drinking fuel like a thirsty camel anymore. The idle is smooth as silk too. Best part? It cost way less than I expected. Really appreciate everyone's input on this. It definitely helped me ask the right questions when I was at the shop. Cars can be such a headache sometimes, but it feels great when you finally get to the bottom of the problem!