I have same problem. Changed so many things but I still have same problem. Did you find out what was the problem?
Mine does this on my Mack from time to time, I usually pull over, hit the parked regen button, let her do a parked regen while I take a 50 minute nap, then it's fine for 2 or 3 months. Usually mine says I have poor quality DEF. But since I only get DEF in our yard, we know that's not the problem.
Peeing in the def tank always seemed to keep it toped off. And saves the company a ton. I was told its basicaly the same thing...
You will never run low...wont get cougjt with your pants around your a ankles trying to pee in the def tank when you find out your empty and def not working at your fuel stop.
I’ve gotten into several new trucks where previous driver reported problems. Not any more. Top it every time. No exceptions. Trucks that idle too much will have problems, and bad spec (too much engine) will also. Cut the idle time to nothing, and assuming best spec for work description, never have to think about re-gen or DEF-related. In 50k on latest truck I’ve never seen re-gen lamp lit (390k total miles). Last truck, same (91k at end). As a practice, how can it hurt? Adds no time to buying fuel. And NEVER worried about de-rate. Running low starts the problem cycle. I keep an eye on consumption per X-miles.