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lesvraissavent · 10-28-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

Got a code saying intake manifold pressure too high (overboost detected during regeneration) since then truck doesn’t ask for regen and now I get nox efficiency low and poor def quality every 10 days, I do manual regen and code goes away.

Changed def filters about 2 years ago and truck did regen back then now it never asks for any regen.

Any ideas?

hhow55 · 10-28-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

What is the maintenance schedule for def filter?

hhow55 · 10-28-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

http://rawze.com/forums/showthread.php?tid=34

lesvraissavent · 10-28-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

(10-28-2022 )hhow55 Wrote: What is the maintenance schedule for def filter?

It was changed along with dpf filters and 7th injector about 2 years ago about 150,000 miles have passed by

What worries me is that truck doesn’t ask for regen ever since that intake manifold pressure too high code

lesvraissavent · 10-28-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

Truck is 2016 cascadia dd15 with 590,000 got it at 430,000 and replaced dpf filters as they were at 99 percent

hhow55 · 10-28-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

https://rawze.com/forums/showthread.php?tid=475

This may help

tree98 · 10-29-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

It shouldn't be asking for a regen unless something is already wrong. If the system is in good working order it will be passively regen'ing and you wouldn't even know it unless you happen to see the hi exhaust temp light on.

hhow55 · 10-29-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

A visit to Mr Hag, would be worth your while.

hhow55 · 10-29-2022, **(Subject: 4364 Fmi 18/ Poor Def )**

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RE: SPN 4364 FMI 18?
this means that the nox reduction from the aftertreatment inlet and outlet nox sensors is not high enough. in otherwords the scr isnt working. if you drive it long enough with this issue it will get steadily increasing derates until your down to 1000RPM.

Most of the time it is a bad nox sensor. it can also be a bad scr injector, bad urea, urea crystals in the decomp tube, wrecked SCR, bad dosing pump/plugged filter, or a leak in the urea system.

force a regen and compare inlet to outlet nox - when the scr is dosing the outlet nox should be much lower than the inlet nox (outlet should run about 25ppm).