The Ram Cummins 6.7 is equipped with a Selective Catalytic Reduction (SCR) system. The SCR system requires the use of Diesel Exhaust Fluid (DEF). DEF is injected into the SCR catalyst where a reduction reaction occurs, converting nitrous oxides into water and nitrogen gas. This reduces both the EGR and DPF regeneration duty cycles. When a truck is new with low mileage this system works relatively well. If your having issues with your DPF & SCR and dont want to spend thousands of dollars only to have it fail later on down the road; consider removing it completely and doing a DPF/SCR delete.