Cummins Fault code 3226.4

Hello, I have a freightliner m2 business class 2012 6.7 Cummins Eng for anyone reading this in 2025 who would like to solve this issue. It’s most likely going to be with your DEF system and not likely your Nox sensor. You can change it, but I would recommend oven cleaning your DEF filter because it may get clogged up and not allowing the DEF to properly escape through which triggers the nox sensor. I forced regen the def but it only temporarily stopped the issue. If you change the sensor and the check engine light is still on, it’s because the truck isn’t able to regen when it’s supposed to because of the sud. Try cleaning your def filter and letting it regenerate before changing your sensor