DPF Diesel Particulate Filter: what it is and what you need to know about it

The rise in popularity of diesel engines in the last 20 years combined with ever tougher exhaust emissions laws has meant manufacturers have had to come up with new ways to make their cars cleaner. The DPF Diesel Particulate Filter DPF is one such solution. But what is it and what does the DPF mean to drivers?

What is a DPF Diesel Particulate Filter?

The Diesel Particulate Filter is a component situated within the car’s exhaust system. They have been compulsory in all diesel vehicles sold in the EU since 2009. They are designed to remove the harmful particulates, visible as smoke, that a diesel engine produces. The idea is to leave only filtered emissions to enter the atmosphere.

How does the DPF work?

The DPF contains a filter designed to trap the soot produced by the combustion process. It consists of a porous ceramic material arranged in small channels that the exhaust gases pass through. Soot builds up on the filter surface and is then burnt off by a process called regeneration. This is done automatically by the car every 300-500 miles when on a long journey.

DPF Diesel Particulate Filter
How a DPF works (Picture © Vauxhall)

Why does the DPF go wrong?

Despite their popularity in small city cars, diesel engines with DPFs don’t like start-stop journeys. This is because soot collects in the filter but the exhaust doesn’t get warm enough to burn it off. If the regeneration process is never triggered, the DPF can become clogged. An orange warning light (below) will then illuminate on the dash. Leave that unchecked and it will tell the engine’s Electronic Control Unit to stop the engine or put the car into limp-home mode.

DPF Diesel Particulate Filter

Can you fix the problem without visiting a garage?

If you notice the DPF warning light has come on you should be able to get the car to perform the regeneration cycle yourself. All you need to do is take it on a longer journey at speeds higher than 40mph for around 20 minutes. The DPF will then be able to automatically burn off the accumulated soot and should start working normally again.

There are also products available from motor retailers that claim to help clean a DPF. They work by assisting in the combustion and burning of the soot in the DPF. They will get good results but can’t overcome the fundamental problem of the exhaust not getting hot enough.

Can DPF trouble be prevented?

You can stop any DPF problems by ensuring your diesel vehicle isn’t only used for short start-stop journeys. A long run every couple of weeks should ensure that the filter can clear itself. If you can’t manage this, your DPF will become fatally clogged. Should this happen, it will need to be replaced which can cost anywhere from £400 to more than £1000 depending on where you go and what type of part you use. Before buying a car, consider what kind of journeys you’ll be doing. A diesel may not be the best solution for short journeys or a life at low speed in a congested city. Have a look at cars with small petrol engines instead.

If you can’t get the DPF light to go out, find a garage to put it right here

Mandy Weston

Mandy Weston

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