Diesel Particulate Filters

Diesel vehicles have become increasingly popular across the world as diesel engine technology continues to advance due to their superior fuel economy over petrol vehicles. The drawback with diesel vehicles however, is that they have high NOx and particulate emissions compared to their petrol counterparts. In response to this, existing Euro Emissions Standards were tightened and greater environmentally friendly initiatives were developed, such as the implementation of ‘Stop/Start’ technology in many modern vehicles. One of the most prominent developments however was the introduction of Diesel Particulate Filters (DPFs).

What are they and how do they work?

The Diesel Particulate Filter is part of the exhaust system which helps reduce the amount of harmful particulate matter (soot) expelled within exhaust gases. It captures and contains these particles and when soot levels inside the filter reach their allowed limit, the Regeneration process is initiated, burning off any trapped particles and converting them into carbon dioxide.

Exhaust gases containing soot enter the DPF channels which are closed off at alternating ends. The channel walls are porous, allowing exhaust gases to pass through, but retaining (trapping) the larger soot particles inside the DPF. Cleaner exhaust gases then exit the DPF as the trapped soot particles are reduced to smaller ash particles during Regeneration. The Regeneration process also helps to prevent blockages and is integral to the function of the DPF and therefore the vehicle.

We manufacture DPFs to cover a huge range of vehicles including:

Alfa Romeo, Audi, BMW, Chrysler, Citroen, Dodge, Fiat, Ford, Honda, Hyundai, Jaguar, Kia, Lancia, Lexus, Mazda, Mercedes, Mini, Mitsubishi, Nissan, Peugeot, Porsche, Renault, Saab, Seat, Skoda, Suzuki, Toyota, Vauxhall/Opel, Volkswagen, Volvo

What are they made from?

  • Cordierite DPFs look quite similar to Catalytic Converters. Cordierite is an ideal material for DPFs as it filters out a large percentage of particles and is very thermally stable and often used in aftermarket products.
  • Silicon Carbide (SiC) DPFs are constructed from small sections cemented together. SiC has superior hardness, low thermal expansion and good thermal shock resistance. It tends to be used in OE applications and is classed as a Premium product.

Over 50% of our standard range of DPFs are available in the Premium range which is denoted by the “P” suffix.


As the DPF acts as a “soot trap”, a process needs to take place to prevent it becoming blocked and affecting the running of the vehicle. This is the process of Regeneration. There are 3 different types of Regeneration – Passive, Active and Forced. Regeneration “burns off” (oxidises) the particulates that have accumulated in the DPF:

  • Passive Regeneration is a process of soot reduction via natural conversion. It occurs when ideal driving conditions apply (60mph for 15 minutes – e.g. motorway driving). The DPF becomes hot enough to burn off some of the trapped particulates naturally between 350-500°C. The carbon soot particles are converted into carbon dioxide by a reaction with nitrogen oxide using the coating of the DPF, which works as a catalyst.
  • Active Regeneration occurs when the optimum exhaust gas temperatures can no longer be maintained, meaning Passive Regeneration can no longer take place. Therefore, Active Regeneration is an ECU led process that increases the exhaust gas temperature to 500-800°C. When the carbon soot deposits in the filter reach a certain level, the engine management system initiates the Regeneration process which lasts around 10 minutes. DPFs can hold several hundred miles worth of soot before this process is initiated. The ECU may also trigger vehicles into limp mode to help protect other components when it senses that the DPF is becoming blocked.
  • Forced Regeneration involves very high temperatures and is carried out by garages with diagnostics equipment.

WARNING! The very high temperatures applied during Active and Forced Regeneration can lead to an accumulation of ash, otherwise known as ‘ageing’. The build-up of ash is treated by physical intervention such as chemical cleaning, ultrasonic cleaning or replacement of the DPF.

DPF Technologies

These days, most diesel vehicles employ one of more different built-in systems to treat exhaust emissions and reduce the levels of soot being emitted during use. These include:

  • Delayed fuel injection to increase the temperature of the exhaust system
  • One or more diesel oxidation Catalysts to work alongside the DPF
  • An additive system which lowers the temperature at which soot combusts
  • Alternative technologies such as microwave or heater coils to raise the temperature within the DPF
  • Exhaust Gas Recirculation or Selective Catalyst Reduction technologies

DPF Maintenance and Repair

It is unusual for the DPF to be the cause of a vehicle fault so it is important to ensure any underlying faults are rectified before replacing a DPF. Below are a few tips to bear in mind regarding DPF maintenance and repair: