How to take care of your diesel particulate filter

The DPF makes your diesel more environmentally friendly - but do you know how to look after it?

Diesel cars are brilliant for families and well known for their huge amounts of mileage. But to drive a cleaner diesel, there's a trade-off in the form of the diesel particulate filter, or DPF.  

All diesel cars since 2009 have been fitted with a diesel particulate filter (or DPF) in the exhaust to meet strict European emissions laws and targets. 

The DPF works like a catalytic converter and traps the solid particles produced by the diesel engine in a honeycomb matrix, stopping the soot from passing into the atmosphere. But there's a catch.

To enjoy the benefits of a frugal diesel, the soot caught in the filter has to be burnt off regularly to keep the DPF working. When the levels in the filter reach a certain point, the DPF has to go through a regeneration process. 

As long as the DPF periodically cycles through this process of trapping particles and then burning them off, you'll likely have no issues with it.

The best way to kickstart this regeneration process is to regularly floor your car down the motorway - a good 30-50 minute blast at a constant speed will allow the DPF to heat up enough that the regeneration can take place. 

Your car's Engine Control Unit (ECU) often aids in this process through 'active regeneration', and injects extra fuel into the engine to raise temperatures further.

You'll know when the regeneration process has started when you hear a slight change in the engine and the cooling fans have kicked in - you might also note an increase in idle speed and a hot smell from the exhaust.

The regeneration can take anywhere from 10-30 minutes, and you shouldn't turn off the engine while it's taking place.

The DPF and the regeneration process isn't something you need to worry about on a daily basis - but you do need to watch out if your driving habits have changed during the pandemic.

Short runs are the mortal enemy of the DPF; the engine doesn't heat up enough for the regeneration to kick in, and the soot particles can build up to a level where only a garage can get it sorted.

To prevent this, make sure you aren't only nipping to the shops or driving the short distance to work. A good long drive regularly will sort the DPF right out and keep your motor ticking along smoothly.

If this regeneration process doesn't happen when it needs to, a light will illuminate on the dashboard to let you know. As soon as this DPF light shows up, it's time to take the car for a good, long spin.

If you don't, the regeneration process won't happen and an engine warning light will appear. At this point, you'll have to get the car to the garage so they can do a Service Regeneration, and your car might enter a 'fail-safe' mode and limit the engine speed to ensure the DPF and the engine aren't damaged.

But if you're regularly taking your car on good long journeys at a good speed, there's no need to worry, and your DPF will take care of itself.