Could be so many things. What is your DEF level? Someone will need a scan tool or computer to get the data, then see what is out of range. There is a pressure sensor before the DPF and 1 after, NOx in and out sensors, temp sensors..... One would think that it would have set some other codes. Upstream problems can cause issues in/with the aftertreatment such as air intake or exhaust leaks.
You could pull out the DEF doser. They can get carboned up or dried/powdered DEF all around it.