A Diesel Particulate Filter is a filter specially designed to remove soot from a diesel engine. If a truck runs faster than 20mph when the filter is full, the engine will start a regeneration process to burn off the collected particles. But after each regeneration cycle, a small amount of soot and ash is left behind, ultimately clogging the DPF.
When the DPF filter becomes clogged, deleting the DPF is not a solution, as it can result in substantial fines. Buying a new DPF is also not an option, new Diesel Particulate Filters being very expensive.