Diesel Particulate FilterA diesel particulate filter separates particulate matter from the exhaust gases produced by diesel engines. Two different systems are in use at Volkswagen depending on the model: diesel particulate filters without an additive are fitted on models where the filter is positioned near to the engine. On models where such a positioning is not possible, systems with an additive are used. The filter with a catalytic coating works without an additive thanks to a coating containing precious metals which fulfils a dual function. Passive regeneration slowly and gently converts the particulate matter contained in the catalytic converter into CO2. This process occurs at temperatures between 350 and 500° C and can run continuously without the need for intervention, particularly in cars which are driven mostly on the highway. Only when vehicles are operated for prolonged periods at low engine loads - as in the case of city driving - does additional filter regeneration have to be carried out by actively raising the exhaust temperature to around 600° C every 1,000 to 1,200 kilometres. At this temperature, the particulate matter trapped in the filter burns off. On additive-based systems, the additive serves to reduce the particulate ignition temperature to around 500° C. Regeneration needs to be performed every 500−700 km, depending on driving style. The additive is automatically flushed into the fuel tank every time the driver refuels, with one litre of additive lasting for approx. 2,800 litres of fuel.