Dpf Additive Systems Explained

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The most commonly fitted type of DPF has an integrated oxidizing catalytic converter and is located very close to the engine where exhaust gases will still be hot (600-650°C). This heat means that passive regeneration is more likely to be successful.

Some models, across a wide range of manufacturers, use a different type of DPF, namely FAP which relies on a fuel additive to lower the ignition temperature of the soot particles.

FAP is the brand name of the particulate filters fitting in cars made by Peugeot-Citroen-PSA. This type of filter was the first to be installed on standard production cars (the 2.2 HDI Peugeot 607 engine). Use was later extended to 2.0 HDI and gradually installed on an increasing number of cars, including those of the FIAT-PSA joint venture (Ulysse-Phedra). From a technical point of view, FAP belongs to the type of filters which require the use of additives (cerium oxides, iron oxide, etc.). Eolys is the brand name of an additive. These were the first filters to be installed on cars and therefore are also the one which are best known, in terms of problems, servicing methods and repair procedures.

As previously mentioned, the filter regeneration process consists of burning the particulate collected by the trap. The particulate is burnt at a temperature of approximately 600-650°C. In order to reach such temperatures, modern diesel engines carry out post-injections after TDC which burn on the oxidising catalyser arranged in front of the filter. The purpose is to increase the temperature of the exhaust gases.

  • Example of post injection strategy


On the FAP systsem the additive is appropriately added to the fuel to lower the regeneration threshold by reducing the particulate combustion temperature to approximately 450°C. The gas temperature reaches 450°C with the post-injections to that the particulate inside the filter is burnt and the filter is regenerated.

The additive is stored in a separate tank next to the fuel tank and is automatically mixed with the fuel whenever you fill up. Only very small quantities are used so a litre of additive should treat around 2800 litres of fuel – enough to cover 25,000 miles at 40mpg. It lasts about 70000 miles and is replenished during a service – at extra cost.

  • Example of a FAP system layout


  • A. Engine
  • B. Common rail
  • C. High pressure pump
  • D. Engine ECU
  • E. Fuel pump
  • F. Level indicator
  • G. Injector and adjuster
  • H. Fuel tank
  • L. Additive
  • M. Muffler
  • N. Sensor
  • P. Particulate filter
  • R. Pre-catalyst

You will have to pay to get the additive tank refilled at some time in the car's life – expect to pay between £150 and £200 including fluid and labour

  • DPF vs FAP


Don't be tempted to ignore a warning light showing that the additive tanks need refilling. It's absolutely essential this tank is refilled as without it regeneration is unlikely to be successful and a new DPF may be needed – at significant cost. Fuel consumption can increase as a result of failed regeneration's too.