SCR Performance low, engine will derate IN..

What engine? Year make model would help

 

On mine it was the Nox sensors after the dpf and the doc were cleaned. That's one possibility.

 

usually nox sensor s need to be replaced, i have a collection of about 50 of them hanging up

 

Both nox sensors should run around 1200 with labor and all this is usually the first thing i do now when i see this derate come up, i have not seen any kind of wiring do this you can try to replace the def filters as well shouldn't be to costly there is two on on the pump and a tiny filter in the line going to injector, most of the time i have seen this fault it has been from nox sensors also sometime like winter time when people left trucks running overnight in chicago this came from excessive idle i would force a couple of regens and it would lift the derate, nox efficiency could be anything on the engine from egr being messed up and letting to much exhaust in or egr cooler being plugged to turbo injectors could cause this as well, if you run a regen monitor how it does the regen and if all temps and everything looks good. that would be a starting point and see if that gives you anything

 

did you idle a lot before this came up on the dash.