Dpf failing

I’m not sure what that code is specifically, that would help. Black spot on exhaust pipe, where? There’s quite a few junction points. That could be anything from a lose clamp to maybe a ill functioning egr valve, to a clogged doc/dpf causing high back pressure.

You should be able to plug into a computer and check the after treatment backpressure readings to check the status of the dpf/doc. The filters tend to be in that $3000 range, and even cleaning them can result in mechanic damage to the filter, cracking it, and causing a needed replacement. I’d say, check the code- see what it stands for and check the computer read out for after treatment back-pressure; to see if it’s within tolerance or out of spec

 

3251 is only the SPN part of the code. What FMI are you getting?

 

Off the top of my head ( not fact checked) 3251 is a after-treatment inlet pressure code. If thats the case, and with the sound it’s making, this is probably the case.
If it where my truck, I would take the DPF out and DOC and blow them out backward with shop air and put it back together if the DOC’s cant be removed, figure out a way to attach a vacuum to the front of it and vac while you blow. ( you may want to do this anyway to reduce the mess. Put it back together and see what you got.

You can do this without a computer and see if the code “heals itself” after this operation.

This won’t address the reason for the soot but this might save your, exhaust system for the time being.