Diesel Particulate Filter - Acknowledgement

Diesels produce lots of soot (particulate matter) that can cause respiratory problems and contribute to the risk of cardiovascular diseases.

Modern diesel cars (since 2009) have to be fitted with a Diesel Particulate Filter (DPF) in the exhaust to stop this soot passing into the atmosphere.

The aim is an 80% cut in particle emissions but the technology’s not without problems and our patrols are often called to cars with a blocked DPF.

To maintain performance a DPF has to be emptied regularly. This is usually done passively in a process called ‘regeneration’: when the exhaust temperature’s high enough, on motorways or fast A-roads.

The collected soot is burnt off, leaving only a tiny ash residue.
The ash can’t be removed – unless the DPF is removed from the vehicle and sent away for specialist cleaning – but a DPF in a car used correctly should be good for well over 100,000 miles.

Active regeneration

Many cars don’t get the right sort of use for passive regeneration to work so car manufacturers build in ‘active’ regeneration where the engine control software senses that the filter’s getting blocked and injects extra fuel into the engine to raise the exhaust temperature and trigger regeneration.

Active regeneration will be initiated every 300 miles or so depending on how you use your car and will take 5 to 10 minutes to complete. But it’s a problem if your journey’s too short and the regeneration doesn’t finish.

During active regeneration you may notice:

Cooling fans running
Faster engine idle speed
Automatic Stop/Start doesn’t work
Increased fuel consumption
A hot, acrid smell from the exhaust.
The engine sounds different

Don’t ignore a warning light

If you get a warning light showing that the filter’s blocked, it should be possible to complete an active regeneration cycle and clear the warning light by driving for 10 minutes or so at speeds over 40mph with more than a quarter of tank of diesel.

If you ignore a DPF warning light and keep driving in a relatively slow, stop/start pattern, soot will build up in the filter until your car goes into ‘restricted performance mode’ to prevent damage.

If you let it get this bad:

Driving at speed alone won’t be enough.
You’ll have to get a dealer to do a manual or ‘forced’ filter regeneration.
In extreme cases they may have to replace the filter which can cost at least £2,000 which you will be responsible for.

In most cases there’s only a short time between the DPF being partially blocked and it getting so blocked it needs a manual regeneration at a main dealer garage.

You might need to change your driving style to keep the system working properly. Follow any advice in your vehicle handbook but in particular what you need to do to carry out a normal regeneration is:

Occasionally go on a longer journey for 10 minutes or more at speeds at or above 40mph
Low fuel level – an active regeneration won’t take place if you have less than 1/4 tank of fuel. Make sure you have enough
If warning light on the dashboard appears please call First Flexi Lease immediately for advice.