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Diesel Particulate Filters

Did you know that more and more new diesel cars are being fitted with Diesel Particulate Filters? As its name indicates, this is a type of filter which removes sooty particles from the exhaust gases of diesel vehicles. These particles are often visible on older diesel vehicles as black exhaust smoke. Diesel Particulate Filters have a similar function to a catalytic convertor, fitted on most petrol-engine cars. Manufacturers are increasingly using this technology in order to comply with the increasingly strict EC regulations for exhaust emissions.

How do they work?

As with any filter (think of the bag in your vacuum cleaner), Diesel Particulate Filters have to be emptied regularly to maintain performance. This process is called 'regeneration' – the accumulated soot is burnt off at a high temperature to leave only a tiny ash residue. There are two ways in which regeneration takes place:

  • Automatically on prolonged runs (such as motorway drives) when the exhaust temperature is high
  • By the Engine Control Unit (ECU) making small adjustments to the engine settings during shorter journeys

In some cases, the regeneration warning light may appear if the driving style is insufficient to allow full regeneration to take place. It should be possible to clear the warning light by driving for a period of 10/15 minutes at speeds greater than 40mph. However if the warning light continues to show, the vehicle will need to be taken to a dealership for repair work to be carried out.

What should I consider before getting a car with a Diesel Particulate Filter?

Driving constraints in locations such as inner-city (continual stop/start) and islands (eg Channel Islands, Isle of Man) are unlikely to facilitate regeneration. Please consider your driving style and normal driving conditions to determine whether a diesel or petrol engine car is best suited to meet your needs.

Where can I find more information?

If you do buy a car with a Diesel Particulate Filter fitted, it's important to read the relevant section of the manufacturer's handbook so that you understand exactly what actions to take if the warning light illuminates and how, if at all, your driving style may need to be adjusted to ensure maximum efficiency and life for your Diesel Particulate Filter.