Diesel Particulate Filters: what is a DPF and which cars come with one?
All modern diesel cars are fitted with a Diesel Particulate Filter (DPF). We explain what it is, why your car needs one and how to keep it maintained
If you drive or are considering buying a diesel car, there’s a good chance you’ve heard of a diesel particulate filter (DPF), and terms like DPF regeneration. A diesel particulate filter is vital to keeping toxic diesel-specific emissions down, but if you’re not careful they can get clogged and cause issues. Basic knowledge of how diesel particulate filters work and how to clear one will help you avoid DPF-related problems if you drive a diesel car.
Many diesel drivers are unaware of how their driving style can affect how their DPF works, so it’s important to take this into account to keep your car healthy. Diesel particulate filters need to regenerate (‘regen’ for short) to avoid clogging, but this can only happen by driving around for extended periods of time. This is why we don’t recommend diesel cars for drivers who make shorter, more frequent journeys around town where the car doesn’t fully heat up. DPF regeneration is extremely important to prevent causing issues with your filter, which could prove expensive to repair – extreme clogging could even cost more to repair than the car is worth in some cases.
DPFs are not the only way manufacturers are trying to make diesels less polluting; many cars built since the introduction of more stringent Euro 6 emissions regulations came in 2016 use AdBlue or systems such as selective catalytic reduction to achieve this.
What is a DPF filter?
Unlike in a petrol combustion reaction, diesel releases a lot of soot when it’s burned as a byproduct of combustion. Because soot can cause big issues for the environment and people’s health, the DPF’s job is to catch it before it gets released into the atmosphere. DPFs have been mandatory on diesel cars since 2009, but many diesels sold before that date were sold with them already.
While a DPF’s first job is to trap and hold onto harmful particulates, it needs to get rid of them, too. The DPF does this by exposing them to very high temperatures, burning them and turning the particulates into harmless ash, in a process called DPF regeneration. This is why diesel cars need to be driven for extended periods of time to allow the system to get hot enough to operate correctly. It’s recommended that you take your diesel car on a long drive on the motorway for half an hour or longer at least once a month.
DPF regeneration: passive and active
The DPF can start regeneration in a couple of ways, but both need the exhaust gases to get extremely hot – usually around 500 degrees Celsius. As a result, diesel cars aren’t particularly suitable for people who only do short journeys - perhaps just around town - because the exhaust doesn’t get hot enough for regeneration to occur, meaning soot builds up and the DPF can’t get rid of it. Eventually, the soot will block the DPF completely and cause engine problems like reduced fuel-efficiency and misfiring
‘Passive regeneration’ takes place when you drive your car at speeds above 40mph for a period of time, and doing this regularly should burn off the particulates in the DPF automatically.
If you don’t drive at speed often, the engine will try to clear the DPF via ‘active regeneration’. This is where the engine lets the exhaust gases get hot enough to burn off the soot without requiring the car to be run at speed. Some diesel engines are designed to do this more often than others.
Unfortunately, active regeneration can only take place when the car is moving, so town drivers – who typically drive in stop-start traffic – may find their cars are unable to actively regenerate the DPF.
Most cars have a two-stage warning system. If you see an amber light, you should be able to get the DPF to regenerate itself by driving over 40mph for about 10 minutes. If you see a red DPF warning light, however, this means you need to pull over to the side of the road and phone your breakdown company to take you to the garage.
If the DPF light comes on, it’s usually a warning that the device needs cleaning. You can check our helpful guide to dashboard warning lights here. Your car’s handbook will tell you how to drive in order to make this happen. If you follow these instructions and the light doesn’t go out, you need to take the car to a dealer as soon as possible. While it’s possible to buy DPF cleaner fluids from car spares shops, the jury is out on how effective these are and DPF cleaning is a job best left to the professionals.
Depending on how badly blocked the DPF is, the dealer may be able to use special DPF cleaner products and techniques. If it doesn’t offer this service, ask if the DPF can be removed and sent to a specialist firm for cleaning. This process should cost around £100 – although the garage will obviously charge you for removing and refitting the filter.
If you’re unlucky, excess soot may have damaged the DPF beyond repair. If this is the case, it will have to be replaced and DPF replacement cost can be as much as £2,000 or more. Shopping around for an aftermarket DPF could save you some money, however.
List of cars with a DPF
As mentioned above, all diesel cars produced in or after 2009 will have a DPF, while larger cars and trucks may have needed one fitted much earlier to comply with 2004’s ‘Euro 4’ emissions targets. If you’re not sure, you can find out if your car has a DPF by looking in the handbook. If your car requires an oil with a low ash content, that can also signify that it has a DPF.
All VW Group 1.6-litre diesels produced before 2009 have a DPF, including any Skoda Greenline models. Volvos produced after 2006 will almost certainly have a DPF, and all Land Rovers from 2010 (including the Range Rover Evoque) have them. 1.6-litre and 2.0-litre Ford TDCi engines have a DPF, as do the majority of Kias built from 2008.
Should I consider DPF removal?
No. While there are plenty of unscrupulous individuals offering a DPF delete or removal, doing so will only end badly. Not only will you be causing unnecessary damage to the environment, your car will automatically fail its MOT test because it’s emitting more harmful gases than it should.
One final word of caution: if you own a diesel car, make sure you know how to get your DPF to regenerate, so you can do it as soon as you see the warning light come on. Stopping the car (which you’ll need to do to consult the handbook) can make the blockage worse. And, if you frequently turn off the engine while the DPF is going through the regeneration cycle, it can lead to severe engine damage.
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