iQ NOx Catalyst Aging and Exhaust Leak

The symptoms you describe, the check engine light, the NOx catalyst aging error, and the exhaust leak, strongly suggest a problem within your exhaust system. The error code is a direct indicator of a potential issue with the catalytic converter's efficiency. An exhaust leak can indeed cause this, as it disrupts the delicate balance required for proper catalytic function. Is your fuel efficiency impacted?

Thanks for the quick reply! I think the fuel efficiency has dropped a bit recently. Could the leak alone cause the NOx catalyst issue, or is it more likely the catalyst itself is failing?

The exhaust leak, particularly if it's located upstream of the catalytic converter, is the most probable cause of your NOx catalyst inefficiency. A leak introduces excess oxygen into the exhaust stream, throwing off the air-fuel mixture that the catalyst needs to function correctly. Prolonged exposure to this imbalance can accelerate the catalyst's degradation, giving the impression of aging. I suggest having the exhaust system professionally inspected to confirm the location and severity of the leak. A workshop will be able to pressure test the system. After that, they can re-evaluate the NOx catalyst's performance. Do not keep driving with an exhaust leak.

Okay, that's really helpful information. I'll get the exhaust system checked out as soon as possible. It turned out to be a cracked exhaust manifold that cost 265€ to repair. Thanks again for the guidance!