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Diesel Particulate Filter (DPF)

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A diesel particulate filter removes particulate matter (soot) from the exhaust gases of a diesel vehicle. It is normally used with a catalytic converter. A DPF can remove over 90% of soot and so ensure no visible soot is emitted from the exhaust tail pipe.

Vehicle manufacturers have to meet emission legislation and the Euro V standard means nearly every diesel car in Europe has a DPF fitted. No DPF now means an MOT failure so if it’s removed, it has to be replaced, but it’s ok because Autosessive can help!

If your DPF is in need of maintenance, specialist products can be used to clear out soot blockages without dismantling, like Wynn’s DPF Cleaner or Wynn’s DPF Regenerator.

How does a DPF work? Here’s the technical bit…

Diesel Particulate Filters have a porous cell wall. Gasses are forced to pass through this wall to exit the DPF Filter. Any solid particulate matter gets trapped inside the filter, because the holes within the wall are not large enough to let it pass through. This means only clean exhaust gasses will exit the filter.

Over time soot builds up inside the DPF. This build up will occur faster when exhaust temperatures are low, which is why build up will occur more quickly during short journeys, city traffic and stop/go journeys. As the DPF becomes more clogged, the amount of back pressure in the system will increase, leading to a loss of engine power and poorer fuel economy.

If the DPF becomes too blocked the vehicle will either stop or go into ‘limp home’ mode. Fortunately the MIL light should show to warn that the filter is becoming blocked before this happens. A blocked filter needs to be ‘regenerated’. There are two types of DPF regeneration – passive and active.

Passive regeneration happens automatically during long or high speed journeys, as high exhaust temperatures burn off the trapped soot. However, as not all vehicles regularly undertake long journeys, active regeneration is sometimes needed. This happens when soot reaches a pre-determined level. Here the ECU adjusts the fuel injection timing to increase exhaust temperatures and so burn off the soot.

An illuminated MIL doesn’t necessarily mean that the DPF is blocked. There are many reasons why an MIL will be on, such as a blocked EGR pipe, turbocharger wear, too much engine oil in the engine or an ECU fault. It’s vital that all possible causes of the lit MIL are investigated first, before the DPF is regenerated or replaced. We've created a handy infographic to help you through the steps to find out if your DPF needs replacing. would always recommend that a DPF is fitted by a qualified technician. If the correct fitting procedures aren’t followed, a new DPF could become blocked in as little as 30 miles and it won’t be able to regenerate.


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