What is a DPF and does your car have one?

If you own a diesel car, chances are it has a DPF. It's a topic we get lots of questions about on a regular basis and DPF problems can cause a real headache.

What is a DPF?

A diesel particulate filter (or DPF for short) is part of a diesel car's exhaust system that's designed to filter out harmful soot.

Diesel engines produce a lot of soot when they burn fuel. This soot is what's known as particulate matter. It’s a very fine substance that can cause serious health problems, namely breathing problems. 

The job of the DPF is to filter and store this soot in order to reduce emissions from diesel cars. But because they have a limited capacity, this soot has to be regularly burned off to regenerate the DPF.

If the soot blocks the filter, this can stop the engine from running and leave you with a hefty repair bill for either cleaning, or worst case scenario, replacing, the DPF. It's no surprise we get some many questions from readers about DPFs.

Does my car have a DPF?

If it was built after 2009 then it will do. All diesel cars since September 2009 have to be fitted with a DPF in the exhaust to stop this soot passing into the atmosphere. It's part of the Euro 5 standard for diesels but be aware that some cars built before this date also come with DPFs.

What does a DPF actually do?

The job of the DPF is to filter and store soot from diesel engines. So what does it do with all that harmful soot? The DPF burns it off the filter at high temperatures, leaving a residue of ash behind. This is what is known as regeneration. 

Regeneration burns off the excess soot in the filter, reducing harmful exhaust emissions and helps to prevent the black plumes of smoke you sometimes see from older diesel vehicles when they accelerate. There are two types of regeneration - active and passive. 

Passive regeneration

This takes place while driving, using the heat of the exhaust. Doing this on a regular basis is enough to burn off the soot and turn it to ash. However, it requires the temperatures created when a car is running at speed for a sustained period of time.

To make sure that the regeneration takes place, it's advised that diesels are driven for a good 30 to 45 minutes on a motorway or A-road at a constant speed.

However, passive generation isn't always possible, for instance if you sit in lots of traffic. So car manufacturers have designed active regeneration.

Active regeneration

Active regeneration works by injecting extra fuel in order to increase the the temperature of the exhaust gases and burn off the soot in the DPF. It still requires a journey of a reasonable length though - around 10 minutes at 40mph or more is the suggested time.

How do I know if my DPF is regenerating?

When the DPF is regenerating you may notice the the cooling fans running and higher fuel consumption. The tell tale sign for many is a hot and unusual smell from under the car. The engine idle speed can also be higher than usual. If your car has start-stop, you'll likely find that it's deactivated during regeneration.

Why do DPFs get clogged up?

DPFs get clogged with soot if regeneration doesn't happen often enough. If that's the case you'll get a DPF warning light come up on the dash. This usually happens to drivers of older diesels that do lots of short trips, or lots of start/stop driving, because the vehicle doesn't get up to a high enough temperature to achieve passive regeneration. Cars with active regeneration should see fewer DPF problems.

How do I prevent my DPF from clogging up?

You need to ensure your DPF regenerates in order to stop it clogging up with soot. That means driving it a sustained speed for 30 minutes or more. How often you should do this depends on the kind of driving you're doing but if you sit in a lot of traffic, a good motorway or dual-carriageway run at 60mph once a week will burn it off.

Active regeneration will be initiated every 300 miles or so depending on how you use your car and will take around 5 to 10 minutes to complete.

What happens if you ignore a DPF warning light?

If your DPF becomes clogged with soot, you will get a warning light on your dash. Driving at a sustained speed in order to burn the excess soot off is often enough to clean the DPF and solve the problem without needing to visit a garage.

But if you ignore this warning light, the car will eventually go into limp mode to prevent further engine damage.

If left any longer, the DPF won’t be able to regenerate itself and will need to be cleaned or even replaced. 

You should also ensure you use the right engine oil. Certain oils contain additives that can actually block DPFs. Using low-quality fuel and running the car frequently on a low fuel level can also harm a DPF because the car may avoid regeneration in order to save fuel.

How much does it cost to clean a DPF?

Some garages can clean a DPF using forced regeneration. Costs vary but as a guide, Halfords offers a DPF deep clean for £85. It involves special cleaning agent being injected into the filter to remove the soot blockage.

Where can I get my DPF cleaned?

If your DPF light comes on and driving it at speed doesn't solve the problem, it may need cleaning. There are plenty of places you can get this done without it breaking the bank. Here are the companies to look at if you need your DPF cleaned.

Halfords AutocentreHalfords

A well know name, Halfords Autocentre has two DPF cleaning options available, depending on the seriousness of the fault - a maintenance clean and a deep clean. Halford uses Ceramex technology to clean DPFs.

How much does a Halfords DPF clean cost?

Prices start at £35 for a maintenance clean which is designed for drivers who make lots of short trips, where the engine isn't getting hot enough to burn off excess soot. It is a preventative treatment that works by lowering the point at which the soot burns off. The deep clean is another £50 but includes a special cleaning agent injected into the filter to remove the blockage. For extreme cases, Halfords offers a complete clean where the DPF is removed and soaked overnight. It will be sent to a specialist if need be.

Product 

Price

Details

Maintenance Clean

£35

Designed to be used every 6 months

Deep Clean

£85

For heavy soot build up

Complete Clean

POA

Removal of DPF and overnight soak 

TerracleanLogo _45358bdcdb 7d 1086766b 0c 287382da 39_1x

You'll often see the Terraclean name cropping up if you're searching for DPF cleaning services. Unlike Halfords it doesn't have centres itself, but its DPF services are available through a network of more than 500 approved centres and mobile technicians. 

How much does a Terraclean DPF clean cost?

You can find your nearest Terraclean service centre from the Terraclean website. Prices vary according to different garages, but Terraclean says it sets recommended retail prices for a standard preventative maintenance service -  vehicles up to 2000cc are £110 while those above 2000cc are priced at £130.

Product 

Price

Details

Preventative Maintenance Service

£110

Cars smaller than 2.0-litre

Preventative Maintenance Service

£130

Cars above 2.0-litre engine size

Engine Carbon CleanEngine -carbon -vlean -logo

Engine Carbon Clean is a mobile service which has local agents across the UK and offers a DPF cleaning service alongside its carbon cleaning service.

How much does an Engine Carbon Clean DPF clean cost?

The DPF clean for cars and vans is a three stage process typically taking between 2-4 hours and includes a full diagnostic check and report which is normally £49. The price includes travel to your location, handy if you want it done at home or while you're at work.

Product 

Price

Details

DPF Clean

£199

Includes a diagnostics check

Turner DiagnosticsTurner _Logo

Founded in 2007, Turner Diagnostics claims to be the longest established DPF cleaning specialist. The company is based in Hemel Hempstead, not far from the M25

How much does a Turner Diagnostics DPF clean cost?

The company charges £84 an hour to diagnose the problem and find out what has caused the DPF to fail and become blocked. It says it can normally diagnose most problems within an hour. To clean the DPF costs £265 which includes resetting the soot level calculation in the ECU.

Product 

Price

Details

DPF Clean

£265

Diagnostics charged at £84 an hour

Doctor CarbonUntitled -1 (15)

Doctor Carbon is another company that offers a DPF cleaning as part of a mobile service alongside engine carbon cleaning. It covers an area from London up to Scotland with teams based in London, Peterborough and Sheffield.

How much does a Doctor Carbon clean cost?

The DPF cleaning process costs £199 and can be done at your home or workplace for no extra charge. According to Doctor Carbon it takes 'around couple of hours' and it guarantees that the filter will be cleaned after. 

Product 

Price

Details

DPF Clean

£199

Mobile service at no extra charge

How much does a replacement DPF cost?

If you don't maintain the DPF properly, excess soot can damaged the DPF beyond repair. If this is the case, it has to be replaced - and they're very expensive. A new DPF can cost anywhere from £1000 up to £3500. There are DPF suppliers that charge less, but make sure they have the correct Type Approval or they may not work properly and end up costing you more in repairs.

How long should a DPF last?

A DPF can last up to around 100,000 miles if maintained properly. After the car has exceeded that mileage, you could be looking at paying a large amount of money for a replacement - so always properly check MoT and service records when buying a used car. Otherwise, you could end up forking out for unexpected repairs on high mileage diesels.

Can I remove the DPF?

No - it is illegal to drive a car that was designed to have a DPF without one fitted. This is because should you remove it, your car no longer meets its emissions standards. Owners face fines of up to £1000 for cars and £2500 for vans if caught. Removing a DPF can also invalidate your car insurance policy.

From February 2014, checking the presence of a DPF became part of the MoT test procedure. All cars that are designed to have a DPF now get inspected for one. If it’s missing it will mean an immediate failure.

Is a DPF covered under warranty?

Most manufacturer's warranties don't cover the cost of DPF replacement if the fault is deemed to have been caused by the owner's driving style. Given that a replacement DPF costs around £1000 it's not hard to see why manufacturer's aren't keen to cover them.

There are lots of factors in the lifespan of a DPF such as the annual mileage of the car, the oil used and what manufacturer's would call 'the driving style' of the owner. We are yet to hear of anyone being able to get a DPF replaced under warranty.

Ask HJ

How long do I need to drive at speed to get the DPF to regenerate?

I owned an Evoque that had issues with the DPF. But when a diesel flags up that the DPF needs a regen, how long time or distance wise do you have to get it on a motorway/dual carriageway before the fuel is dumped into the sump? Would it not be better for drivers to have a gauge so they can plan ahead for it?
Because the DPF is under the car, not 'close coupled' in the exhaust manifold, the car needs to be driven quite a long way (50 miles) at 2000 - 2500 rpm to get the DPF hot enough to promote a passive regeneration. An active regeneration will happen automatically, but if the DPF is too stuffed up with soot for this to work, the post-injected diesel intended to fire off an active regen will instead sink into the sump.
Answered by Honest John
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