Noah NOx Catalyst Aging Exhaust Leak

Interesting. I had something similar happen with my Noah – not sure what year yours is, but the symptoms sound familiar. That NOx catalyst is a pain. The exhaust leak is a big clue, though. Think of it like this: if you're trying to bake a cake in an oven with a hole in it, it's not going to bake evenly, right? Same principle with your emissions system. If the exhaust is leaking before it hits the catalyst, it’s going to throw everything out of whack. Have you checked the gaskets and flanges really closely? Sometimes those can corrode and cause a sneaky leak.

Thanks for the reply! Good analogy with the cake. Makes sense. When you say gaskets and flanges, are there any specific areas I should be focusing on? I gave the whole system a once-over, but maybe I missed something subtle. Was your error code the same? And did the leak end up being the root cause?

Yeah, my error code was indeed related to the NOx catalyst efficiency. Check the connection points closest to the engine first, then work your way back to the catalytic converter itself. Pay special attention to any areas that look rusty or have soot buildup – that's usually a good indicator. Honestly, though, if you suspect a leak and you're seeing that code, it's probably best to get it up on a lift and have a professional take a look. I ended up having to take mine to the shop, and it turned out to be a small crack in a weld that I just couldn't see properly at home.

Appreciate the advice, especially confirming that the leak could trigger those NOx catalyst errors. I took it to the shop as you suggested. Turns out, there was a hairline crack in the exhaust manifold, causing a leak. They welded it up, replaced a gasket, and the error code is gone. Total cost was 265€ Thanks again for pointing me in the right direction!