Check Engine Light and Exhaust Smell

I had a similar issue with my Mini not a Countryman, but still. Check engine light and exhaust smell inside the cabin. I'd start by visually inspecting the exhaust system for any obvious cracks or leaks before condemning the NOx catalyst or catalytic converter. Is it running rough or just showing the light?

Thanks, that's helpful. It's running fine, no noticeable difference in performance. Just the check engine light and the error code related to NOx storage catalyst aging. Where exactly on the exhaust system did you find the leak?

Mine was a crack in the exhaust manifold, pretty common apparently. Since you smell exhaust, it's almost certainly a leak somewhere. The sensor readings get thrown off, which can trigger the NOx catalyst error. Best bet is to take it to a workshop and have them do a smoke test to pinpoint the leak.

Thanks for the insight. Turns out it was a cracked exhaust manifold. New one fitted, total cost 265€. Hopefully, fuel efficiency will improve now, and the emissions system will be happy.