The Mazda 6 DPF (Diesel Particulate Filter) is designed to trap soot also known as particulate matter from escaping the exhaust system into the atmosphere. It’s a great idea and works extremely well by reducing soot particles by up to 90%. In fact, it works a bit too well, so well that eventually it will block up and cause endless problems for the owner of the vehicle and until now, the only option was to replace the DPF with a new one which again will be waiting to get blocked again.
There is a process known as regeneration which your vehicle should do without your input, automatically every 200-300 or so miles which basically increases the temperature of the exhaust gasses to help burn off any soot trapped in the Diesel Particulate Filter box to unblock it so it can continue to work, however, this is not very effective and they continue to get blocked up to a point where even a forced regeneration is not possible.
Once the DPF has failed and a regeneration is not possible, your local dealer/garage will advise you buy unit. A new one will cost you in excess of 2000+ with parts, labour & vat. Buying a used / 2nd hand DPF is never advised as it will come partially blocked already and waiting to fail again. In fact, even with a new unit on your car it will not bring you complete piece of mind because the design of the Diesel Particulate Filter has not changed one bit, so you will be waiting for it to fail again.