the diesel engine fluid (def) system is essentially the same as the dpf, except it uses def instead of diesel fuel. Similar to the dpf system, the def system removes soot from your engine and stores it in a canister located within your exhaust system in little ‘honeycomb’ shaped compartments. When too much soot builds up and needs to be cleared, this system goes into a regen cycle and uses def at a high heat to burn off and blow out the built up soot.
Not only does def reduce fuel efficiency and performance, a def delete service for your diesel engine will remove this system so your truck is running at peak efficiency and performance. Trucks with the def delete install can improve fuel efficiency by up to 30%