Citan NOx issues

I had similar problems with my emissions system on a 2018 Vauxhall Astra, although not the exact same error. An exhaust leak can definitely mess with the readings from the oxygen sensors and throw off the whole emissions system. Has your fuel efficiency taken a hit? Is the smell of exhaust stronger than usual?

Yes, fuel efficiency seems slightly reduced. Regarding the exhaust system leak, where was the leak on your Astra?

Mine was at the flex pipe, a common failure point apparently. Since you have exhaust leaking and NOx errors, I'd strongly suggest getting the exhaust system checked professionally. It could save you money in the long run and is better for air quality anyway.

Thanks for the insight. I took it to a workshop, and it was indeed a leak in the exhaust system. Repair cost 265€. Problem solved.