Poor Def Quality SPN 3364 FMI 2 DD15 Cascadia EVO 2014 (2024)

I have same issue malfunction light and check engine light comes on when I am at high altitude same code comes up 3364 fMI 2. I've changed nox countless times, doser valve, doc outlet and Inlet. No one can tell me why it comes on only when I climb a hill at high altitude. Comes on at exactly the same spot everytime. Derate me to 55mph. Drive with check engine light on and when I go up the next step hill sometimes the check engine goes away. If not I do a regen and it goes away. Malfunction light goes away eventually. I've been everywhere and they always say its nox, never fixes it. Please help

I have same problems. No one can tell me why. Whenever I go up 15 Frey in california and I hit 4000 feet elevation the two lights come on, malfunction and check engine. Also blinking def light. Sometimes it goes away and sometimes I have to do regen. I've replaced box so many times bc dealers say it's that. 860 dollars and then light comes back on. Replaced doc outlet and inlet sensors, replaced doser valve, nothing works. If I drive in the city or flat grounds never comes on. It only comes on when I climb. Please help

New 1-box needed...

Aftertreatment is a big issue. I have seen a lot of engine with poor def quality, I have tested the def and all the time it test good(otc 5025 def refractometer $70) Most of the time it's an intermittent issue (communication between sensors and ecu). Why it comes on only when you climb, I don't have an answer for that. One advice, try not to let the def level go to low to the point you get a warning. I have seen sometime that the def light will come one with poor def quality. If you can do a parked regen and it completed successfully you are good to go. If not try to get to the nearest shop have them scan for codes and have them clear codes and perform a scr / regen test if everything pass the code will become inactive and have them clear the code and you can be on your way for about 2 hrs labor. before you start spending money. Now if the code is still active they have to do proper diagnostic the replace the part that is bad.. I hope this is helpfull!

Outlet nox sensor is the culprit......
For def bad quality always change outlet nox sensor first instead of changing all other parts. .....

Have changed box sensor countless times. Changed inlet and outlet doc sensor recently. Emission light comes on when I climb and always in the same spots. Got codes spn 5246 fm0, 4364 fmi18, spn3364fmi2, spn5246fmi15, and spn5246fmi16. Long time ago tech said he enlarged holes for def to spray better do you think this could be why?

On my truck after changing SCR outlet nox sensor. not doc sensor .no more bad quality and low conversion codes. truck runs fine 8 months now.

Sometimes mechanic wants to make more money .they dont put your scr outlet nox sensor until they changed everthing.it happens with me same .then i forcefully order my mechanic to change scr outlet nox sensor but my mechanic not happy with that.but it work for me.thats why iam here sharing my story.

I have the exact same issue. Have spent 8k replacing sensors harnes doser pump ect. Still comes on when going up steep hill, and eventually goes away after driving 20-80 miles at 55 mph. Has been doing this for a year and a half.