Sorting Out Your SPN 4331 FMI 16 DEF Pressure Problem
Seeing spn 4331 fmi 16 pop up on your dash is never a great way to start a shift, especially when you've got a long haul ahead and a deadline to meet. If you're staring at that code right now, it basically means your truck's brain thinks the Diesel Exhaust Fluid (DEF) pressure is running higher than it should be. It's categorized as "Data Valid but Above Normal Operating Range - Moderately Severe Level." In plain English? Your SCR system is under too much pressure, and if you don't deal with it, the truck is probably going to start cutting your power to protect itself. ...