Help w Fault codes

[tree98]

(02-23-2021 )Zondo956 Wrote:  Been having fault code 5868 and 3749 coming on for a while. About 6 months ago. Did a egr tune up and replaced outlet nox sensor and def doser injector. Usually saw them when temp was 20-40 degrees outside. Now they’re coming on at any temp. Intermittently and go away.
I was told to change out def level/quality/sending unit.
Any suggestions?

What DEF are you using? Have you ever checked it's quality with a refractometer? Maybe check your SCR for DEF crystal buildup. Have you been using more DEF than you should be?