What is a diesel particulate filter (DPF)?

A diesel particulate filter traps most of the soot produced by a diesel engine, preventing it travelling down the exhaust and out into the atmosphere where it can cause breathing problems, particularly in cities. DPFs are required by law in Europe.

Why do DPFs need to regenerate?

Just like the filter in your household vacuum cleaner, which can’t hold an unlimited amount of dust, a car’s diesel particulate filter will eventually become full with soot and therefore requires emptying on a regular basis. This process is called regeneration, the trapped particulates getting burned off. Regeneration occurs automatically and generally kicks in when the car’s DPF has reached a suitable temperature, which allows the soot to be converted into a more compact volume of ash.

The risks of infrequent regeneration

Cars not driven in a style that makes regular regeneration possible are exposed to dangerous levels of soot building up, which will affect the vehicles’ performance and also result in DPF damage, unless something is done about it.

A warning light is usually displayed by vehicles fitted with a DPF. Ignoring the warning can result in serious damage to a car or van and because it will be treated as neglect, the vehicle’s warranty won’t cover the cost of repair. Lease car drivers failing to follow the recommended DPF regeneration process can incur business costs of £1,500 or more and will have to visit a dealership for regeneration to be forced.

Image courtesy of Renault

How to regenerate your car’s DPF

  • It varies between makes and models, but the general rule is to drive the vehicle at a speed of at least 50mph for 20 miles or more
  • This is so that your vehicle’s engine and its internal gases reach a high enough temperature for regeneration to automatically begin
  • Occasional hard acceleration is also often suggested, allowing a vehicle to ‘clear its tubes’

If you live in a city, taking the time to travel to the nearest fast A-road or motorway is better than facing an expensive 4-figure repair bill. Don’t worry if there’s a slight smell whilst regeneration takes place.

Isn’t there an easier way?

A small number of makes and models are fitted with self-heating DPFs that don’t require fast, sustained driving to start the regeneration cycle, instead injecting fuel directly into the filter, the fuel burning and therefore increasing the filter temperature. Certain vehicles alternatively feature heaters built into their DPFs. Our car leasing and contract hire consultants will be more than happy to advise you on how certain vehicles work in this respect.

Image courtesy of Vauxhall
Image courtesy of Vauxhall

What does this all mean for you?

In short, if most of your driving is in slow-moving urban traffic, a petrol, hybrid or electric vehicle without a DPF will almost certainly be better for you. High-mileage motorway drivers generally shouldn’t have many problems with DPFs, as driving at around 70mph over sustained distances ensures that DPF regeneration occurs, keeping engines clean and running smoothly. Business fleet managers looking after any number of company cars are more than welcome to contact us for advice.