Mini Countryman exhaust treatment issue

Oh my, an exhaust treatment malfunction sounds incredibly worrisome! I had a similar issue with my Mini Countryman recently, though the symptoms weren't exactly the same. Check engine light was on, yes, but I didn't notice any leaks or strong smells. The engine was definitely running rough though, almost like it was struggling. Have you checked the particulate filter? What about the EGR valve? Is there any chance it could be related to the catalytic converter?

Interesting. You mentioned a similar issue. When yours was running rough, did you also experience any exhaust smell, or notice any leaking? And did you end up needing a new lambda sensor, or was it something else?

No exhaust smell for me, thankfully! And no leaks that I could detect. It was indeed the oxygen sensor. The mechanic mentioned that a faulty oxygen sensor can cause all sorts of problems with the exhaust system. If you are smelling exhaust and hearing leaks I'd strongly advise against driving it until you get it checked out by a professional. You don't want to risk damaging the catalytic converter or other components. Hopefully, it's just the oxygen sensor for you too, but with the added symptoms, it might be something more complex. Is taking it to the workshop a possible option for you?

Just wanted to circle back and say thanks for the insight. Turns out it was a faulty oxygen sensor as suspected. Got it replaced, and the Countryman is running smooth again. Cost me around 375€, but worth it to get rid of that awful smell and the rough idling.