DD15 emissions help!!!

Help with what? Have new box put on, get the he** down the road.

 

If that's the "black box" or "one box" it's gonna be pricey....$10k or so.....I've been told.

 

That code is a SCR NOX Conversion Low. I'd say 85% of the time this is due to a failed SCR in the one-box. Could be a lot of things, but if they've checked everything and not found anything, an internal failure of the SCR is most likely.

 

That code is a regulatory code that has a strategy for getting at least 80% NOx conversion I think. Somewhere around those values. Usually the SCR can get poisoned. Depends what type of oil you run...what type of fuel. Sulfur is the killer here.
You're getting the code because your OTR regen is failing.

 

The catalyst is no longer active / contaminated and or DEF fogging is insufficient. DEF problems are repairable fairly cheap. The catalyst side is very expensive. Detroit now is allowing for a scrubbing of the DOC faces plus vacuuming the contaminants (there's an actual Detroit vacuum tool). There is also another option that Detroit is now allowing and that is a "burn off" for the DOC. The truck computer system needs to be updated for this. If this does not work you will need to replace the 'one box'.

 

what is the mileage of your truck ? were dpf filters cracked inside?