Maintain the emissions system on your 2011-2016 Chevy/GMC 6.6L LML Duramax with Diesel Exhaust Fluid (DEF) System components. Replace the damaged components in your system with the quality options available including DEF heaters, fluid pumps, and control modules. Diesel engines use a selective catalytic reduction system that injects DEF directly into the exhaust stream to convert nitrous oxides into water and nitrogen. Leading brands such as Dorman offer the components needed to maintain the Diesel Exhaust Fluid (DEF) System on your vehicle.