DTC P20EE00 on Volvo D13 related is to SCR system, causing DEF crystallization and clogged DEF dozer valve or muffler, this is the DIY fix ,problem solved. Owner operator on parking lot,done. @branstz
I had similar problems, I changed from flex pipe to nox sensor, clamps and gaskets, but still it didn't help, I went to dealership and one guy told me since your truck has 1.8 milion km it's catalyst that is giving you a problem, change it, it will fix your problem, he said rather buy used one from some truck with low mileage than aftermarket, I changed catalyst and all problems related to scr and dpf are gone. New catalyst in Canada is 8000$, I found good used one for 3K.
Of course if you tested def doser valve and show ok, but still you getting the same problem than is usually worst scenario your dpf filter is bad or have some cracks and need to be replaced
