SPN 4334 FMI 18

This very same code SPN 4334 fmi 18 showed up on my 2018 freightliner m2 106 tow truck.
I checked and cleaned out the DEF lines nothing wrong with them.so at that point I ordered the DEF DOSER ran the truck for a bit and it seemed to fix the problem.drove the truck for a day and the code came right back.diagnosed it same code SPN 4334 fmi18,at that point it’s gotta be the DEF PUMP so I ordered and installed it,I ran the truck for a bit and it cleared the code.
So I drove it for a few more days and sure enough the code came right back but this time there was a circuit code for the Low DEF PRESSURE.
So I searched the wiring harness from the DEF DOSER I found that the wiring harness because it’s so long Cummins had to loop a portion of the wiring harness and it was laying on top of the PTO where it flattened and actually chaffed the wires.
So I moved the harness away from the PTO and the problem was solved.
And that’s after I spent 3k in parts before I found the problem.

 

Truth ! had the same code come up on my 2023 , truck running fine , thought this thru walked to the truck,removed the DEF filler cap,stuck my pointer finger and pushed the flap open, this released the pressure, started up the truck, codes cleared. got lucky .. EZ fix

 

I'm currently getting this code and scr de-rate. I don't have a count down timer though. Will I eventually be derated to 5 mph without the counter?

 

It will if it stays active.

 

Mine just popped up 4334 fm 3 OC1

 

Out of curiosity, would a new def filter fix this issue? On my 14 cascadia, I replaced it to fix a similar code. They're pretty cheap and easy to replace.