My DPF light is on, what does it mean?

DPF light is on

All new diesel cars sold in the EU since 2009 – even posh ones like the Bentley Bentayga (above) – have a DPF or Diesel Particulate Filter. This is a component located in the car’s exhaust system that’s designed to remove the harmful particulates, visible as smoke, that a diesel engine produces.

What does it mean when the DPF light is on?

The DPF contains a filter designed to trap the soot produced by the combustion process. This soot builds up on the filter surface over time. It is then burnt off by a procedure called regeneration. This is done automatically by the car every 300-500 miles when on a long journey. The warning light comes on if the filter is getting clogged.

DPF light is on
If this lights up, going for a 20-minute drive should clear the filter and turn the light off

What might happen?

The orange warning light is designed to warn you that the DPF needs attention. If left unchecked it will tell the ECU to put the car into limp-home mode. This means you’ll notice a drop in engine power and responsiveness. The car may not start unless you rectify the problem.

Read why you don’t have to warm a car up

Can you fix the problem without visiting a garage?

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 automatically burn off the accumulated soot and should start working normally again.

Do products from shops work?

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.

DPF light is on
Here is how a DPF works, according to Vauxhall

Why does the DPF get blocked?

Diesel engines with DPFs don’t like start-stop journeys. Soot collects in the DPF but the exhaust doesn’t get warm enough to burn it off. If the regeneration process is never triggered, the DPF becomes clogged.

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. Don’t do this and 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. If you are looking to buy a car that will only do short journeys or spend most of its life at low speed in a congested city, a diesel may not be the best solution. Have a look at cars with small petrol engines instead.

Can you remove the DPF?

A simple fix used to be for garages to remove the DPF altogether. No DPF, no problem. However, this has been outlawed. If your car was built with a DPF and a garage detects that one is no longer present, it will automatically fail its MOT.