Had an interesting one at work the other day on a euro 6 LF chucking on the eml light and going into limp mode. The new ones have egr and ad blue. Haven’t really had any really involved issues with one yet. Daf technical was pointing towards the cat or a nox sensor or ad blue quality. It had are trusted ad blue in it so that was ruled out. We can do a lot with the workshop diagnostics so we road tested it loaded. You can monitor exhaust temp before and after the cat. Nox level before and after the cat. Engine torque and fuel pressure as they only make high nox when working hard. The laptop also works out a nox conversion percentage which ends up being pretty much zero. That had a new cat in the end. I’d never buy a modern diesel there to complicated now and cost a fortune. Sell the thing and buy something else. Egr only works on the dafs to aid heating up the engine then the ad blue system takes over as the main emissions system. Still get blocked egr faults though. Always changing egr coolers and cleaning out the system. They monitor pressure in the inlet manifold and exhaust manifold also pressure difference before and after the dpf.
they can only breath on there only waste for so long before it causes a problem lol