All diesel cars are fitted with a diesel particulate filter (DPF), and it’s important that it’s maintained.

A DPF captures and stores soot from the exhaust to reduce harmful exhaust emissions, but they only have a limited capacity. This means that trapped soot must be occasionally emptied or ‘burned off’, this process is called regeneration.

What do I need to look out for?

If the DPF is blocked or a fault develops, an orange light will usually appear on the dashboard. The warning light can vary by manufacturer, so it’s important to check your vehicle’s handbook to know what you’re looking for.

Orange lights are usually warning lights. If the light turns red, your vehicle needs immediate attention and you should stop driving it straight away.

If your orange warning light continues or if more dashboard lights appear, make sure your vehicle is looked at as soon as possible.

How does a DPF become blocked?

Making frequent short journeys at low speeds is the most common cause of a blocked DPF. It is also important to keep your vehicle regularly serviced, and use the oil recommended by the manufacturer.

What do I do if my DPF light comes on?

The best way to maintain a DPF is to allow it to regenerate itself when the warning light appears. This can be done by passive regeneration, which means giving the car a run on a motorway or dual carriageway to allow the exhaust temperature to rise and burn off the excess soot in the filter. It’s recommended that you drive for at least 15 minutes at a speed of over 40mph.

A second option is active regeneration, which injects extra fuel to increase the temperature of the exhaust and is managed automatically by the vehicle’s computer.

What happens if the DPF isn’t regenerated?

Not fixing DPF issues could result in more damage, which can be costly. It may put your car into a safe mode, limiting the performance of the engine and some models may not restart after a number of miles with the DPF warning displayed.

A DPF check is also part of the MOT, and if the filter has been removed or is blocked, the car will fail.