BMW X4 NOx Catalyst Issues, Power Loss & Starting Problems

Hey there! I have some experience working on cars and dealt with something very similar on my 2016 BMW X3 last year. Those symptoms sound exactly like what I faced, engine light, power issues, the works. Mine turned out to be an exhaust leak near the catalyst. Took it to my trusted workshop and they found cracks in the exhaust system. The whole repair, including parts and labor, cost me around 265 Euro. Really worth fixing quickly because these issues can get worse and cause more damage. I'd be happy to share more specific details about the repair process, but first, could you tell me your car's mileage and whether you've noticed any specific smells or unusual sounds? Also, when did these symptoms first start? This would help determine if you're dealing with the same issue I had. By the way, if you own an X4, you probably already know this, but these BMWs are great cars when properly maintained. My X3 has been running perfectly since that repair.

Thanks for sharing your experience! My X4 just hit 130848 KM and had its last service about 3 months ago. The symptoms started showing up gradually over the past couple weeks, but got really noticeable in the last few days. I do notice a slight sulfur smell, especially when starting the car in the morning, and there's a kind of rattling noise from underneath when idling. The cost you mentioned seems reasonable, I was honestly expecting much worse! Did you experience any issues after the repair was done? Also, how long did the whole repair process take? I need to plan around being without a car for a bit. Thanks again for the help, it's definitely reassuring to hear from someone who's been through something similar.

Hey again! Thanks for those extra details. Yeah, that sulfur smell and rattling noise are exactly what I experienced with my X3 too. My repair actually took about two days, they needed some extra time because they found the cracks had caused some minor damage to surrounding components that also needed attention. After the repair, my car ran perfectly, no more rattling, no smell, and the engine light stayed off. But I'll be honest, I did have a small problem about two weeks later when the engine light came on again. Turned out it was just the system needing a reset, which the workshop did for free. Since then (about 8 months now), it's been running like a dream. Given your mileage and symptoms, it sounds even more like what I dealt with. The sulfur smell is particularly telling, that's a classic sign of an exhaust leak near the catalyst. One tip: if you decide to get it fixed, ask them to check the oxygen sensors while they're at it. My mechanic did that as a precaution, and I'm glad he did because one was starting to go bad. The cost I mentioned earlier was just for the basic repair, but with the sensor replacement and some other minor fixes, I ended up paying a bit more. Still totally worth it though, the car's performance improved noticeably after everything was sorted. Let me know how it goes if you get it checked out!

Thanks everyone for the helpful responses! After hearing about your experience, I feel much better about getting this sorted out. I've actually just booked my X4 in for next week, they said they'll need it for 2-3 days, which matches up with what you mentioned. Really glad to hear your car's been running well since the repair. I'll definitely ask them to check those oxygen sensors too, that's a great tip. Even if it ends up costing a bit more than the initial estimate, it sounds worth it to get everything properly fixed at once. The sulfur smell is getting stronger, so I'm relieved I'm getting it looked at soon. Just hoping it's the same straightforward fix you had and not something more complex. I'll update everyone once I get it back from the workshop. Thanks again for sharing your experience, it's really helped put my mind at ease about what to expect!