BMW Diesel NOx Sensor Nightmare: Real Solutions Inside

Hey there! I have some experience with cars and had a similar issue on my 2013 BMW 3 Series diesel. I totally get your frustration with those NOx sensor problems! I took mine to my regular workshop when I was getting engine codes and failing emissions tests. Turned out it was just a faulty cable connection to the NOx sensor. My mechanic traced it, replaced the damaged wiring and plugs, and recalibrated the system. Total bill came to 95 Euro, not too bad considering I was worried it might be the sensor itself! What's the mileage on your 4 Series? Have you noticed any specific symptoms besides the codes and regen issues? That could help pinpoint if you're dealing with the same problem I had. Btw, their diagnostic showed my 320d had similar regen problems before the fix. Works like a charm now though!

Thanks for sharing your experience! My 4 has 191551 KM on the clock and just had its service last month. I was hoping it would just be a wiring issue like yours, but my mechanic already checked the connections and they seem fine. The regen problems started right after a long highway drive, and I've noticed a slight power loss since then. The exhaust smells a bit different too, kind of metallic. Did you experience anything like that before your repair? I'm worried it might be the actual sensor unit rather than just the wiring in my case.

Hey again! Yes, I know exactly what you mean about that metallic smell, I had that too with my 3 Series before getting it fixed! Looking back at my case, I initially thought it was just the wiring too, but you're describing pretty much identical symptoms to what I eventually discovered was actually a failed NOx sensor unit, not just the connections. When my regular mechanic checked the wiring and found it okay, we ended up having to replace the actual sensor. Cost me quite a bit more than just the wiring fix, around 450 Euro for the part plus labor. But honestly, it was worth every penny because the car's been running perfectly since then. That metallic smell combined with the power loss is really similar to what I experienced. My car had about 178000 KM when it happened. The fact that yours started after a highway drive is interesting, that's exactly how mine began acting up too. The high-speed running probably stressed the sensor to its breaking point. I'd say it's pretty likely you're dealing with a failed sensor unit rather than just wiring. Once we replaced mine, the regen started working properly again, the smell went away, and the power came right back. The engine light cleared up after they reset everything too.

Thanks for the detailed response! That definitely helps confirm my suspicions about it being the actual sensor. What you described matches my situation perfectly, especially the timing with the highway drive and those exact symptoms. It's oddly reassuring to hear someone else went through the same thing, even if it means I'm probably looking at a more expensive fix than I hoped for. I'll get back to my workshop and let them know about your experience, the failed sensor unit causing identical issues with the metallic smell and power loss. At least now I know what I'm likely dealing with and can budget for it. Really appreciate you taking the time to share your story. Did you need to get any other parts checked or replaced while they were doing the sensor, or was that enough to sort everything out?