DD13 recurring code SPN 4364 FMI 18

[uncleal13]

What year and mileage?
What kind of temperatures have you been driving in ?
Are you using a winter front? Factory one or custom one?
That code is a catch all code for low NOx efficiency which can be caused by a lot of different things. The worse one being a worn SCR catalyst requiring a new One-Box, not cheap.
You did say when it’s cold. Detroit constantly says not to use a winter front on these new engines, and yet all trucks I’ve bought come with one. Lately I have discovered, and confirmed with others experience, that the winter front is required in extreme cold.
Down to about -20C (-05F) it is not needed at all, somewhere under that the One-Box cannot get up to a high enough temperature for the NOx conversion to function properly. I get the code you got, or a code for poor DEF quality (I confirmed with a refractometer that it was good). So I put on the factory winter front and everything works as it should.
We had several days down to -40 the other week, -30’s this week and I was good.
DO NOT use a winter front that completely blocks off the air flow.
If the code has gone away the MIL light will clear on its own after a day or two.