DPF (Diesel Particulate Filter)
A DPF is a filter in the exhaust system of every diesel truck built after 2007. It traps soot particles before they leave the tailpipe.
When the filter fills with soot, the truck burns it off in a process called regeneration, which raises exhaust temperatures to around 600C and turns the soot into ash. This happens automatically during highway driving.
A DPF needs regular highway time and correct low ash engine oil to stay healthy. Trucks that only do short city trips clog their DPFs, which leads to warning lights, forced regens at a shop, or eventually a replacement that costs two to four thousand dollars.