BMW 4 Diesel NOx Catalyst Issues & Power Loss Help Needed

Hey there! I have some experience working on cars. I actually faced something very similar with my 2011 BMW 3 Series diesel last year. Just like yours, I had the engine light, power issues, and failed emissions. Turned out I had a leak in the exhaust system, right near the NOx catalyst. Took it to my regular workshop and they found cracks that were causing the problems. The fix involved replacing some damaged parts and sealing the leaks, cost me about 265 Euro in total. After that, the car ran perfectly again, no more warning lights or power issues. Before I can give more specific advice, could you share: What error codes you're getting? Any unusual sounds or smells? Have you noticed higher fuel consumption? I've also owned a BMW 5 Series, so I'm quite familiar with these engines. Let me know those details and I'll try to help further!

Thanks for your input! My car's at 120864 KM and getting into these issues is pretty frustrating. The error codes I'm getting are P2040 and P11B7, and yes, I've definitely noticed the fuel consumption going up lately, seems to be drinking more diesel than usual. No weird sounds that I can tell, but there's this slight sulphur smell sometimes when I start it up in the morning. Had my last service about 3 months ago but these issues started popping up recently. Really hoping it won't be too expensive to fix, but with BMWs, you never know! Fingers crossed it's just something minor like your exhaust leak.

Hey again! Thanks for those details, that really helps paint the picture. Those error codes match exactly what I had with my BMW 3 Series! And that sulfur smell, yep, I had that too, especially during cold starts. In my case, after the initial fix I mentioned before, the problems actually came back after a few months. Turned out the NOx catalyst itself was failing, it wasn't just the exhaust leak I initially thought. The higher fuel consumption is definitely a telltale sign; my car was guzzling diesel like crazy before I got it properly fixed. With your mileage being similar to what mine was (mine was around 125000 KM when this happened), it's pretty common for these parts to start wearing out. The complete NOx catalyst replacement set me back about 1200 Euro, but it was worth every penny. Car's been running like a dream since then. Quick tip: if you're getting it replaced, make sure they check the sensors around it too. I didn't do this initially and had to go back when one of the sensors failed a month later. Could've saved myself some extra workshop time if I'd done it all at once. Let me know what your mechanic says, really interested to hear if it's the same issue I had!

Thanks so much for the detailed response! That's super helpful to know about your experience, especially about checking the sensors too. Bit worried about that 1200 euro price tag, but I guess that's the reality of BMW ownership! I've actually booked it in for next week at my regular workshop, and I'll definitely mention your experience with the NOx catalyst and ask them to check the surrounding sensors while they're at it. Really hoping to get this sorted in one go rather than having to make multiple trips. Your insight about the sulfur smell and fuel consumption being linked to the catalyst makes total sense, at least I know I'm not imagining things! I'll keep you posted on what they find. Really appreciate you taking the time to share your experience and tips. It's always reassuring to hear from someone who's been through the same issues and got them resolved successfully.