Diesel Particulate Filters (DPF): How They Work & Regenerate

14 May 2019
Larry Ficks

In order to comply with the strict emission standards, all diesel vehicles need to be equipped with a diesel particulate filter. The purpose of a DPF is to remove virtually all soot particulates from the exhaust gasses emitted from the engine. With that said, if you’re a diesel vehicle owner, and the filter of your vehicle has become faulty over time or it’s clogged with soot, you should consider replacing or servicing it.

In case you’re unaware of how a DPF works, it basically captures and stores exhaust soot so that it reduces emissions released from your diesel engine. However, like most filters, diesel particulate filters have a finite capacity, which means that the captured soot needs to be burned off or emptied so that the DPF regenerates. Diesel particulate filters can regenerate in one of two ways: actively and passively.


Active regeneration involves extra fuel being injected automatically so that the exhaust reaches a higher temperature and the stored soot is burned off. However, this can only happen if you drive at higher speeds for an extended period of time. If the journey is too short, the process may not be fully completed. If that’s the case, then the orange light indicating that something is wrong with your filter will keep showing. Ideally, you want to drive at speeds higher than 70km/h for at least 20 minutes.

Passive regeneration, on the other hand, happens when you drive your vehicle at high speeds on long distances and the exhaust’s temperature increases “naturally” and it burns off all the excess soot that’s captured in the filter. Some of the signs that regeneration is taking place include a slight increase in fuel consumption, cooling fans start running, the engine’s note changes or there’s a hot acrid smell from the exhaust.


Incomplete regeneration and poor servicing are the two most common reasons why diesel particulate filters stop being effective and why they may fail prematurely. One of the most important aspects of properly servicing and maintaining your diesel particulate filter is using the right type of oil. Some oils contain additives that can block the filters, which is why you should look to use oils that contain low amounts of sulfur, phosphorous and sulfated ash.

All of this is of great importance, otherwise, your vehicle will fail emission tests and you’ll have to pay a huge fine that could have easily been avoided if you properly regenerated or serviced your diesel particulate filter.