I'm in aftertreatment homeschool

[Punchy]

2012 Cascadia daycab with Cummins ISX, popping codes for several months related to the DPF/DEF/SCR aftertreatment system. I don't have Insite at this time, but a heavy duty code reader that gives much info, yet this particular device can't do anything about the problem per se. One code that visits from time to time is 1569/31, which is surely recognized instantly by many.

A breakdown of the canisters and cleaning of filters is a few weeks away as schedule permits. Until then, and up until the moment I write this, we've replaced all temp sensors (the existing temp #3 outlet on what I believe is the SCR can, was actually broken off (disintegrated?) in there when swapped out). The proble still attached to the wire was maybe 5 mm. Some issues disappeared after these replacements.

I've always heard, "don't be a parts swapper just to swap". There's truth to that... I simply want to know what was done to this truck and I don't know/trust the previous owner like that. So, I'ma swap as I play amateur detective. I want to leave this truck better than I found it.

The DEF doser was replaced, and the truck improved still more. However, regens are still unsatisfactory or need to be forced. I suspect that inside this small section of exhaust, right behind the turbo, is clogged or caked over. The V-clamps were nearly welded on. Got those off, and the downside of that exhaust section is able to be loosened from the following pipe which descends to the cans. But, the section connected to the turbo is going to need a chisel to break it loose. They look glued together.

And that brings us to date: The plan is to remove that section which holds the doser and the upstream/inlet NOx sensor there, and see if it's soot-covered up where the new doser needs to be misting.

Attached find a rough diagram of this unit's set-up. Rough = I know I'm way off. I've found that Cummins' diagrams are woefully incomplete and sometimes straight-up blurry, I try to zoom in and it's like 20/100 vision. I'd like help to finetune this over time and hopefully it'll help somebody.

I'm taking all notes.