BMW X5 NOx Sensor Issues: Fix for Failed Emissions Test

Hey there! I had a similar issue with my 2018 BMW X3 last year (I have some experience working on cars as a hobby). When my check engine light came on and I failed emissions, I first tried scanning it myself but ended up taking it to my regular workshop. Turned out it was a loose connection in the NOx sensor wiring harness. The mechanic found that the cable connection was defective and needed to be properly secured and partially replaced. The fix was pretty straightforward, about 2 hours of work and cost me 95 Euro. The car's been running perfectly since then, no more warning lights or emissions issues. Could you share more details about your X5's mileage and whether you've noticed any performance changes? Also, have you had any previous emissions-related repairs done? This would help me understand if you're dealing with the same issue I had. Let me know these details, and I might be able to provide more specific advice!

Thanks for the helpful info! My X5 is currently at 127326 KM and just had its service last month. I haven't noticed any major performance issues besides a slightly rougher idle. The exhaust smell is what caught my attention first, followed by the check engine light. Your experience sounds quite similar to what I'm dealing with. Did you notice any exhaust smell before the repair? I'm hoping it's just the wiring harness like in your case, sounds way better than having to replace the entire NOx sensor unit. I'll definitely get it checked out by a workshop soon. Better safe than sorry with these emissions systems!

Hey again! Yeah, now that you mention the exhaust smell, I definitely noticed that too before getting mine fixed! It wasn't super strong, but there was this distinct smell, especially when idling. The rough idle you're experiencing is exactly what I had too. It's like the engine wasn't running as smoothly as it should, right? After dealing with my X3's issues, I've actually learned that these NOx sensor problems are pretty common in our BMWs. The wiring harness seems to be a weak point in the design. In my case, the smell went away completely after the repair, and the idle smoothed out too. Just a heads up, when I first noticed the symptoms, I waited a couple of weeks before getting it fixed (big mistake). The longer you wait, the more stress it puts on the catalytic converter, which could lead to bigger problems. The repair cost for my wiring harness issue was way cheaper than what a new catalytic converter would have been! Have you noticed if the smell gets worse when the engine is warm? That was another telltale sign in my case. Honestly, from what you're describing, it sounds exactly like what I went through. Let me know how it goes when you get it checked out!

Thanks so much for the detailed follow-up! You've actually made me feel a lot better about this situation. Yes, the smell does get worse when the engine warms up, exactly like you described! I definitely won't make the mistake of waiting too long to get it fixed. I've already called my regular workshop and booked it in for tomorrow morning. It's really reassuring to hear that your repair was relatively simple and affordable. I was honestly worried I'd be looking at a massive repair bill! Will make sure to ask them to specifically check the wiring harness first, given your experience. The last thing I want is to end up needing a new catalytic converter because I waited too long. Thanks again for sharing your experience, it's been super helpful! I'll try to remember to post an update once I get it sorted out.