Diesel particulate filters (DPF) are devices fitted to diesel vehicles which filter particulate matter from exhaust gases. Diesel particulate filters perform an essential role in reducing air pollution and its health effects, their removal is almost always illegal.
This document gives further information about diesel particulate filters and the legal and social implications of removing them from vehicles.
The inspection of the exhaust system carried out during the MOT test includes a check for the presence of a DPF. A missing DPF, where one was fitted when the vehicle was built, will result in an MOT failure.