Matiz NOx Catalyst Exhaust Leak

Greetings, fellow motorist. Your predicament sounds eerily familiar to an issue I encountered with my 2012 Opel Astra diesel. The symptoms you describe – the CEL illumination, the NOx catalyst error code, and the suspected exhaust leak – strongly suggest a breach in the exhaust system's integrity. This, in turn, compromises the efficacy of the NOx catalyst. I would like to ask, have you noticed any degradation in fuel efficiency, or perhaps an unusual odor emanating from the exhaust?

Hey, thanks for the reply! Fuel efficiency does seem to be down a bit, now that you mention it. I thought I was imagining things. And yeah, there's a bit of a funky smell, especially when I first start the car. Is this definitely a leak issue, or could the catalyst itself just be dead after all these years?

Given the supplementary information concerning diminished fuel economy and the presence of an aberrant olfactory discharge from the exhaust, the preponderance of evidence indicates a compromise in the exhaust system's integrity antecedent to the NOx catalyst. While catalyst degradation is plausible, the leak is almost certainly exacerbating the problem, potentially causing the catalyst to operate outside of its designed parameters, accelerating its demise. I strongly recommend a visit to a qualified automotive service facility for a comprehensive diagnostic evaluation. Do not attempt to repair this yourself.

You were spot on! Took it to the shop, and yup, exhaust leak right before the catalytic converter. New flex pipe and some welding later, the leak's gone, error's cleared, and the car runs much better. Cost me about 265€ Thanks for the help!