BMW X5 NOx Catalyst Issues, Symptoms and Solutions

Hey there! I had a similar issue with my 2020 BMW X3 (also had an X7 before). I have some experience working on cars, mainly basic maintenance and troubleshooting. When I faced exhaust problems, I first noticed a loud noise and performance drop. My check engine light came on too. Took it to my trusted workshop, and they found a significant leak in the exhaust system, specifically around the catalytic converter area. The whole repair, including parts and labor, cost me about 265 Euro. But before jumping to conclusions, could you share more details about: Any unusual sounds you're hearing? Does it get worse when the engine is cold or warm? Have you noticed any unusual smells? The symptoms you're describing could be related to what I experienced, but the NOx catalyst issue might be different. Best to get it properly diagnosed to avoid replacing parts unnecessarily. Hope this helps! Let me know if you need more info.

Thanks for sharing your experience! My X5 is at 42632 KM and had its last service just two months back. I'm actually hearing a rattling noise from underneath, especially during cold starts. The smell is quite metallic, and it's definitely worse when the engine is cold. Once it warms up, the performance improves slightly, but the power loss is still noticeable. The symptoms seem pretty similar to what you described with your X3. I think I'll take it to the dealership since it should still be under warranty. Did you notice any improvement in fuel consumption after your repair? Mine's been drinking fuel like crazy lately. Thanks for the help!

Hey again! Thanks for those extra details about your X5. Yeah, those symptoms sound really familiar. After my X3 was repaired, I definitely noticed a huge difference in fuel consumption, it went back to normal. Before the fix, mine was also guzzling fuel like there was no tomorrow, just like yours. That metallic smell and rattling noise you mentioned? Had exactly the same thing. Just a heads up though, my issue ended up being a bit more complex than initially thought. While the exhaust leak was fixed, they also found that the NOx catalyst was indeed showing signs of premature wear. Since you mentioned yours is still under warranty, you're in a much better position than I was. The dealership should cover all of this. The cold start symptoms you described are spot on with what I experienced too. My X3 would sound horrible on cold mornings, and the power loss was really noticeable until everything warmed up. After the repair, it was like driving a completely different car, smooth, quiet, and back to its normal powerful self. Definitely get it checked at the dealership ASAP. These symptoms tend to get worse pretty quickly if left unchecked. Keep us posted on what they find!

Thanks everyone for the detailed responses. I really appreciate all the insights, especially about the cold start issues and fuel consumption problems. Just wanted to update you, I called the dealership and managed to get an appointment for tomorrow morning. They seemed quite familiar with these symptoms when I described them, which is somewhat reassuring. The fuel consumption issue is really bugging me, so I'm hopeful they'll sort everything out under warranty. I've also noted down all the symptoms we discussed to make sure I don't forget to mention anything to the technician. The rattling noise and metallic smell seem to be key indicators, from what you've shared. I'll make sure to post an update once I get the diagnosis and repair done. Thanks again for all the help and for sharing your experiences. It's been really helpful in understanding what I might be dealing with!