Diesel Particulate Filters


Diesel Particulate FilterDiesel Particulate Filters (commonly referred to as DPFs or FAPs) are becoming a commonplace item on Diesel vehicles. It is a device which removes diesel particulate matter (or soot) from the exhaust gas of a diesel vehicle, therefore reducing the particulate emissions.


How do DPFs work?

Unlike a Catalytic Converter a DPF is not a flow through device, and works by forcing the gasses to flow through the filter. As the channels of the filter are blocked at alternate ends, the gasses are forced to flow through the cell walls in order to exit the filter. As the cell walls are porous, the gasses are allowed to pass through, but the particulate matter is deposited on the cell walls. This ensures that only the clean exhaust gasses can exit, and the particulate matter is trapped in the filter.


Cordierite BM Cat's filters are made from Cordierite, a ceramic material that resembles the internals of a Catalytic Converter but alternate holes are blocked.


DPF Maintenance

DPFs need to be regularly maintained to prevent a build up of soot in the filter. Effectively, they are a “soot trap”, so in order to prevent it becoming blocked and affecting the running of the vehicle, it has to be cleaned. This is done with either the use of passive regeneration or active regeneration. A warning light on the dash will warn the vehicle owner if the DPF is becoming blocked and regeneration is needed.


Passive Regeneration – occurs on long journeys when the exhaust temperature is high and the soot burns off naturally. For vehicles which unfortunately don’t get this kind of use, Active Regeneration is needed.


Active Regeneration – occurs when the level of soot in the filter reaches around 45%. The ECU makes small adjustments to the fuel injection timing and increases the exhaust gas temperature. This increases the exhaust temperature which then initiates the regeneration process, burning away the soot trapped in the DPF.


Some types of vehicle (especially Citroen and Peugeot models) use a fuel additive to aid the regeneration process. The fuel additive is added to the fuel tank every time the vehicle is filled with fuel. It is common in vehicles where there isn’t enough room to locate the DPF close to the engine where the exhaust gasses are hottest. The fuel additive lowers the temperature at which the soot particles trapped in the filter ignite and burn off. This allows regeneration to take place at a lower temperature than normal.


DPF Facts and Fitting Advice

It is believed they will need to be fitted to all diesel vehicles to enable them to pass the upcoming Euro V Regulations.

DPFs are normally used in conjunction with a catalytic converter

DPFs can remove 85% or more of the soot and ensure no visible smoke is emitted.

Too much soot in the filter can lead to increased back pressure and potentially cause damage to the engine.

DPFs are direct fit items and should be fitted following the same advice as when fitting a catalytic converter. Other points to follow are;

  • Do not use exhaust paste
  • Ensure all joints are properly sealed.
  • Ensure the fuel additive tank is full.
  • Check all sensor tubes are free from blockages.
  • Check the fuel injection system is working correctly.
  • The ECU has to be reset by a main dealer or independent garage once the DPF unit has been changed to clear any fault codes/service warnings.