2017 Cascadia DD15 Nox Conversion Efficiency Very Low SPN 4364 Fmi 17

have you changed outlet nox sensor? was it purchased from dealer or on ebay?
i fixed a truck with same problem. The problem was nox outlet sensor. It was replaced 2 months ago and was purchased on ebay. the packaging of sensor was like original detroit sensors have..
also you can let nox outlet sensor sniff clean fresh air by hanging it outside on 1 box and drive like that very long time

 

I had a 2011 DD15 that we worked on for months.. They changed out the Nox sensors, rebuilt the dosing module a few times (ports and sensors were clogged), replaced the DEF fluid, replaced the DEF pump filter, blew out the lines, ran regen after regen.. We even removed the DPF filters and tried our absolute best to clean them out. After we cleaned them, we were able to get it to run a good solid regen, but it clogged again after that. Onlinw I found that the onebox system isn't really all too great, because you have to replace the whole thing if it clogs too much.

I didn't even know you could remove the DPF filters until I started tearing it apart.. Needless to say we ended up *cough* Dele *cough* ting *cough, cough*
The truck works great after a few modules got tuned up.

 

I got same issue. 4364 fmi 17 .and 520372 520371 fmi16 . I think only way is program acm.They call it magic turn. Only close scr. coz . The road too many pot holes.like AZ i40 . i 20-Shreveport, LA the shock can damage SCR crack by little pieces in the one box.we paid many tax . They didn’t fix the road. So just delete it.## epa

 

This is a tough code. Air leaks in the intake or exhaust can cause aftertreatment issues as well as fuel etc..... Also problems within the aftertreatment system. It is more of a process of elimination. You need to have the system pressure/smoke tested or pressure tested at 2-20 psi. Once exhaust gets to the SCR there are 2 things that lower NOx, DEF through the Doser and the SCR catalyst. The SCR is like a catalytic converter on a car. That in itself goes bad over time. You say NOx out is at times higher than NOx in. Very telling. Bad catalyst would almost surely be consistent and not intermittent so that leaves the Doser system. Bad DEF, plugged DEF or pump filter..... Freeze frame data should be checked to see what the data is at the time the code set. There may a wiring problem that cuts off the doser.

 

Just read your post again and more carefully. Obvious the shop does not know what they are doing, only guessing. Like I said in my other post you need the data at the time the code set. There is also a DEF pressure pump and pressure sensor, wiring, control module.... Everything on there has a normal range. The data will tell you what is out of range.

Now looked at your pics. There is the 1231-9. ACM (Aftertreatment Control Module) signal not received or has stopped arriving. Regen not going to fix any NOx problems. Regen is to burn off the soot in the DPF.

NOx efficiency goes low when the ACM loses its signal (stops working, so DEF stops at that point). So the efficiency is only a symptom and not the problem. The problem is the wiring or the ACM.

 

I think I know what’s going on.