I was disappointed that a month after the excellent article on DPF cleaning (Maintaining & repairing catalytic converters & particulate filters, CM, February 2018), Steve Rothwell in Tales from the Workshop changed a DPF that was salvageable. Even if a DPF is completely blocked, it can still be resurrected. As a member of the DPF Doctor group, the organisation has saved hundreds of DPFS for customers. Normally, DPFS only need changing if they are physically damaged, although it is quite common to come across a DPF so blocked that the vehicle will not even run or even start. The chemicals we use dissolve the blockage and allow exhaust gas to escape, which then carries the chemicals further into the DPF, cleaning out the rest of it. We are so confident of our system that we can offer a ‘no clean, no fee’ service.