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JimT

yes, DEF buildup can be cleaned. The cause of such a buildup would probably be a leaky DEF valve.

DPF (7th) Injector does accumulate carbon/soot buildup leading to issues with fuel injectioning exhaust. However you'd be seeing other symptoms/issues if that were the case. Yes, the injector can be removed and it and the orifice can be cleaned of soot buildup. It's a normal part of what we all refer to as an EGR tuneup.

If regen temps were too low then you'd be seeing other faults and/or symptoms. Again, when the aftertreatment system runs into an issue it's default response is "do a parked regen". It's the equivalent to computer tech support scripts asking if you computer is plugged in, did you try turning it off and back on?

Based on your input it's my opinion that the Outlet NOx sensor (or it's wiring) is the most likely culprit. Now, if there's other symptoms or additional fault codes that you didn't mention then that could change the analysis.

As for SCR conversion, it only requires temps of a few hundred degrees. That's why a truck goes into catalyst warm-up mode when you start it up or do a lot of stop and go city driving without a heavy engine load.

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While this site is committed to helping disseminate clear and accurate information and encouraging people to learn and become hands on, you shouldn't go messing around with SOMEONE ELSE'S equipment unless you have the proper knowledge, tools AND PERMISSION to do so. While these systems, for the most part, aren't too complex or difficult to maintain, they do require some tools and knowledge. And some things, such as certain gaskets, need to be replaced when removed. I think it's great you are here looking to learn, but be responsible with how you apply what you learn. And at the end of the day, we're all just a bunch of random guys talking on the internet.