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Diesel Particulate Filter

Do you drive a Diesel car?

If so, do you know what is a Diesel Particulate Filter and do you know how to maintain it? A Diesel Particulate Filter is sometimes referred to as a ‘soot trap’. It is basically a filter designed to catch exhaust soot in diesel cars in order to reduce emissions.

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A Diesel Particulate Filter is also designed to store the exhaust soot it captures, and with limited storage capacity, the trapped soot has to emptied or burned off at some point, in order to regenerate the Diesel Particulate Filter.

What are the symptoms of a blocked Diesel Particulate Filter?

  • You feel a loss of power in your car. The engine goes into ‘limp’ mode.
  • You are also likely to get a strong smell from exhaust fumes.
  • You will probably see thick black smoke coming from the exhaust when you accelerate.
  • The Diesel Particulate Filter warning light will usually appear in your dashboard area.

The symbol for this can vary with manufacturer, but will most likely look like a rectangle with pipes on the ends and some dots in the middle of the symbol.


What causes the Diesel Particulate Filter to get blocked?

Short distance driving at relatively low speeds is considered to be the primary cause of blocked Diesel Particulate Filters. So if you are buying a second-hand diesel car privately, ask what kind of driving the existing owner does. If they live and work in the city, it is likely the majority of their driving is short journeys at low speed.

How long should a Diesel Particulate filter last?

Generally speaking a Diesel Particulate Filter (DPF) should last approx 200,000 km. However, in saying that, good servicing is key to longevity. The other really important factor you need to keep in mind as well is to use the right kind of oil as some oils contain additives that can actually block filters.

How to maintain a Diesel Particulate Filter?

There are two ways to regenerate a Diesel Particulate Filter (DPF) and if both of these fail and you still have problems, you can get the DPF cleaned at select garages with a process called ‘Forced Regeneration’ ( more on that later).

1. Passive Regeneration

This type of DPF regeneration is done by the car itself. However, the car has to be running at speed and on a journey of at least 30 – 50 minutes.

This allows the temperature of the exhaust to increase to a level sufficient to burn off the excess soot in the filter.

So it is advisable to go for a drive like this at a sustained speed for at least 30 minutes regularly to help clean the filter.

2. Active Regeneration

The other type of regeneration is called ‘Active Regeneration’.

This happens automatically when the filter reaches a pre-determined limit.

Extra fuel is injected to raise the temperature of the exhaust and burn off the stored soot.

This process happens as part of the car’s ECU (engine control unit)so it happens automatically.

Does Diesel Particulate Regeneration always work?

Active Regeneration is not always successful. For example, if this process is initiated during a short journey there may not be sufficient time to complete the regeneration cycle.

If this is the case, the DPF warning light will continue to show on your dashboard, indicating the filter is still blocked.

It is then advisable to continue driving for at least 10 to 15 minutes at a speed of more than 40 mph to allow the regeneration cycle to complete.

You will know if the active regeneration is taking place by the following symptoms:

  • Cooling fans are running
  • Engine noise change
  • Idle speed increase
  • Slight increase in fuel consumption
  • Deactivation of automatic Stop/Start
  • Bitter pungent smell from the exhaust

What if the Diesel Particulate Filter warning light stays on? 

If neither passive nor active regeneration work and the Diesel Particulate Filter warning light stays on or changes to a red colour, or if you see additional DPF lights on in your dash area, you need to get your car checked out as soon as possible.

This is to avoid further damage and the increased risk of costly repairs!

Can a Diesel Particulate Filter be cleaned?

Yes, we can clean blocked Diesel Particulate Filters with a process called ‘Forced Regeneration’. While this is not a 100% guaranteed fix, it usually is successful. It removes the excess soot and allows the DPF to work. Once the soot has been cleared the automatic regeneration process as describes earlier can work again.
This usually costs around €100.

Remember it is a failure in the regeneration process that usually causes most of the DPF issues. Once the filter becomes blocked, it increases the emissions and impairs the engine performance. So it is best to follow the steps above to ensure the automatic regeneration process can take place regularly.

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