Kangoo NOx Catalyst Exhaust Leak

I had a similar experience with my old Volvo V70, although it wasn't a Kangoo. Check engine light, emissions errors… turned out to be a cracked exhaust manifold. Exhaust gases were escaping before they reached the catalytic converter, which caused the car to fail an emissions test. Is the exhaust leak you hear constant, or does it change with engine RPM?

The leak does seem to get louder with higher RPMs. Was your Volvo throwing NOx-specific codes, or just general emissions errors? And did you notice any change in fuel efficiency before you found the leak? I'm trying to gauge how bad this has gotten.

My Volvo was showing general emissions codes, nothing specific to NOx. Fuel efficiency was definitely down, probably by 10-15%. Given your symptoms and the RPM-related leak, it's highly likely there's a crack or corrosion somewhere in the exhaust system before the catalyst. You could try and visually inspect the system, but honestly, a workshop with a smoke tester would pinpoint the leak much faster.

Turns out you were spot on. Took it to the shop, and they found a crack in the exhaust pipe right before the NOx catalyst. New pipe and a replacement catalyst set me back 265€, but the Kangoo's running like a champ again. Check engine light is gone, and it passed the emissions test with flying colors!