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If you own a diesel-powered vehicle, there’s a good chance it’s equipped with a diesel particulate filter (DPF); read our guide to learn more about what it is and what it does.

EVER SINCE Euro 5 emissions regulations were introduced in Europe in 2009, carmakers have made it mandatory to fit diesel-powered vehicles with a diesel particulate filter (DPF).


What is a diesel particulate filter?

Diesel contains many harmful compounds, although regulators are mainly concerned about controlling the Big Three: carbon dioxide (CO2), Nitrogen oxide (NOx), and particulates. But reducing, say, nitrogen oxides can see an increase in particulates.

While some car makers have trialled exhaust gas recirculation on diesel engines, this can help reduce NOx emissions because an amount of exhaust gas is being directed back into the engine’s air intake, thus requiring less fresh air but doing so reduces cylinder temperatures and increases particulate matter. And because particulates are carcinogenic (meaning they can cause cancer), we don’t want more of the stuff produced.

We have diesel particulate filters. These things capture and store the particulates (or soot) caused by diesel engines. Because DPFs have a specific capacity, the particulates/soot must be burned off to ‘regenerate’ the DPF. The regeneration process burns off the particulates/soot with a DPF able to reduce particulate emissions by 80% compared with your diesel-powered vehicle.



How do I know if my diesel particulate filter is blocked?

If your car’s DPF hasn’t regenerated (explained below) and has become blocked, you’ll see a warning light like the one shown below.


Why would my diesel particulate filter become blocked?

Simple, you’re driving only short distances and at low speeds. Most carmakers suggest a diesel particulate filter will last around 10,000 Miles before needing replacement.


How does a diesel particulate filter regenerate?

There are two ways in which your vehicle will ‘regenerate’ the DPF (usually once the filter has hit 45 per cent capacity) via either ‘passive’ or ‘active’ regeneration.

Passive regeneration occurs without the driver know when the vehicle is running at high speeds for around 30min or longer. This allows the exhaust temperature to heat up to burn off the particulate/soot.

Active regeneration was introduced to ensure those drivers who only drive a short distance and thus don’t meet the threshold for passive regeneration could still have the particulate in their DPF burnt off.