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

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Truckin4ever77, Jul 5, 2022.

  1. Truckin4ever77

    Truckin4ever77 Bobtail Member

    Nov 24, 2016
    Hi guys,
    I got some issues with the truck, I wanted to see if you might be able to help me give me some direction what it might fix my problem.

    I have 2017 DD15, last month I got problem check engine came on. The def light started flushing and thr truck derated to 55 so I took it to the nearest dealer not far from home. They said first that the truck has code for nox conversion efficiency low and the outlet nox sensor is bad and need update on the modules, but after doing update and replacing the outlet nox sensor again same issue, no changes. Then they said they need to do valve adjustments because the air/fuel mixture is probably rich. They did that and then said again same issue. Next thing they changed the air filter and the air filter box thinking that might help but same thing. Then they said is probably a problem with the One box and the truck needs a new one. I towed back the truck from them and started working on it myself. First I took out all the def fluid and put new one inside and tested to make sure is good. Then I checked the Delta pressure sensor, maf sensor, air intake temperature sensor and HC doser they were never replaced and were all dirty with soot so I changed them with new. I checked the truck with dddl and did regen, the nox conversion is fluctuating, sometimes at the begining at 95-100% then goes down to 0 then around 20-60%. The Doc Inlet pressure is 0.4-0.6 Outlet Doc pressure half of that (around 0.2-0.3). Then I cleaned the DPF filters (2 dpf filters are new from last year) and cleaned the One box, installed them back (the place that cleaned it said the one box and dpf filters didn't looked bad/dirty/plugged at all), installed new inlet Nox sensor, new inlet Doc pressure sensor and hose (the hose was clogged), new soot sensor and did regen but it was same thing. I then installed new def doser but same thing. Tried Doc face plug still same. I had problem with the variable water pump leaking a little and since I see that the normal running temperature of the truck it goes from 205-220F (when the fan turns on at 320-221F), I thought it might be problem with the thermostat so I changed the pump and thermostat. Still same things. The temperature in the dpf goes to almost 1100F but nox efficiency still when starts sometimes is 97-100% and then just goes completely bad down to almost 0% or below 60%. The temperature still the same 205-220f on regen. It bothers me that sometimes it shows perfectly good nox efficiency and then goes bad. The harness from the ACM to the sensors looks good not damaged, checked the ohms were good from the ACM to nox outlet and were showing good. It's like when the truck gets hot the nox efficiency goes bad. The inlet nox is around 400ppm and outlet sometimes goes even more than inlet value. No Def crystalization.
    What it could be the problem do you guys have some idea that can help me? I don't know anymore what to do. I am thinking what if the update on the modules caused the problem (because they got code for nox sensor, but did update and put new sensor)...or maybe the acm is not working properly...or maybe the harness is causing problems when gets hot ... I really am out of ideas.
    Thank you very much

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  3. armo

    armo Light Load Member

    Jun 16, 2022
    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 :)
    LoneRanger Thanks this.
  4. Gonzalexb17

    Gonzalexb17 Bobtail Member

    May 21, 2020
    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.
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