Are you asking what the scr catalyst is or just whether the readings you have are good or not?

 

It sounds your vehicle is a Euro 6 compliant. This means it uses a Selective Catalytic Reducer (SCR) which uses AdBlue to reduce the NOx emissions. However, it would appear that your NOx emission are slightly higher than they should be. It most likely the adblue injector is not injecting enough adBlue into the SCR. It could just be the adblue injector nozzle is partially blocked.

This link shows the typical Peugeot system.

https://www.greencarcongress.com/2016/01/psa-peugeot-citro%C3%ABn-tests-confirm-environmental-performance-of-bluehdi-scr-technology-for-diesel-nox.html

This video may give you an idea of how to deal with the problem

 

Thanks, I'll get the local mechanic I use to take a look when I take it in.

The car itself isn't objecting to anything yet, so I'll leave it be!

 

There are a number of things that can cause scr catalyst efficiency problems, probably best left to somewhere that knows how to test the system properly as the components that make up the scr system are not cheap, ofcourse as above checking and unblocking any crystallised adblue from the injector nozzle can be done but if that didn't improve the ppm, i would be looking to have a professional take a look unless you have alot of time for road testing carrying out drive cycles and reading live data streams

 

Yes good idea. If this is your first Euro 6 engine make sure you know how to top the AdBlue. If it runs out you will get a warning telling you how many miles you have left. If you don't fill it in time it is likely that the engine ECU will not let you start the car.

 

Yes, first thing I did was top that up . Having done some driving around it appears one of the NoX sensors reads 20ppm with the engine off. It then sorts itself once the engine is running. Makes me wonder again whether it's just a false reading that it 20 higher than it should be. Anyway, doesn't make much difference, I'll leave it unless it starts to cause trouble!