Does my car have a DPF (diesel particulate filter) fitted?
DPFs (or diesel particulate filters) make diesels run cleaner, but how do you know if your car has a DPF? How does a DPF work? How do you keep it in good condition and what DPF problems might you encounter if you don’t keep it in tip-top condition?
Well wonder no more. For the answers to all those questions and more, keep reading.
What is a diesel particulate filter?
A diesel particulate filter (DPF) collects the thick black soot produced by a diesel engine – the stuff you've seen spewing out of older diesels under acceleration – to stop it going into the atmosphere.
The soot, also known as particulate matter, has tiny particles that can be breathed deep into our lungs causing health conditions such as asthma and bronchitis.
What is passive regeneration?
Passive regeneration is the technical term for burning off the soot collected by your car’s DPF. It only works on the motorway or A roads (or anywhere you can drive at a high sustained speeds), which give your DPF the heat and time (around 30-40 minutes) it needs to burn off soot. This has caused problems with DPFs getting blocked on cars that are rarely driven on the motorway.
How do I keep my DPF in good condition?
Going for a 40-minute motorway drive is a fail-safe way of keeping your DPF filter in good condition, but there are some other tricks.
One of those is making sure your car isn't always running on an empty fuel tank. Some cars won’t regenerate their DPFs if their fuel is low because it burns more diesel so even if you are on the motorway, your DPF won’t get cleaned.
Another top tip is to make sure you use the oil recommended by your car’s manufacturer, the wrong stuff could contain additives that damage your car’s DPF.
How long should a DPF last?
A DPF should last for 100,000 miles but maintenance is key. The DPF in a car that has been well maintained and serviced correctly will last much longer than one on a car that hasn’t been properly maintained.
How do I know when my DPF is blocked?
If your DPF is nearly blocked, a DPF warning light will flash up on your dashboard – that’s your cue to take your car for a long, fast run so the DPF can burn off soot before it becomes permanently blocked.
Older diesels which do lots of short, slow runs often suffer from blocked DPFs that have to be unblocked manually or even replaced entirely.
What is active regeneration?
Because of these problems with older diesels, manufacturers introduced active regeneration which isn’t so reliant on you taking your diesel car onto the motorway for long periods.
Instead, active regeneration injects extra fuel into your car’s cylinders, increasing the exhaust temperature and allowing the DPF to burn off soot quicker and at lower speeds.
What happens if I ignore my DPF warning light?
If you ignore your DPF warning light for long enough, your car will eventually go into limp-home mode to prevent further damage to the engine. However, you should still be able to begin passive regeneration by taking the car for a long motorway drive. Fail to do that and the DPF will need to be manually cleaned or even replaced.
How much does it cost to manually clean a DPF?
If your DPF becomes permanently blocked all is not lost, places like Halfords can carry out forced regeneration which – for around £85 – clears your DPF by injecting it with cleaning agents. Or you can pay for a more expensive overnight deep soak.
Other companies like Terraclean offer preventative maintenance priced from £110 (engines less than 2 litres) to £130 (cars more than 2 litres) which helps your car burn off soot at lower temperatures to stop the DPF getting blocked in the first place.
How much does a replacement DPF cost?
If none of these treatments do the business, you’ll be looking at paying for a replacement DPF with prices ranging from £1000 to up to £3500.
Can’t I just remove the DPF?
Unfortunately, you can’t just remove the DPF if it’s no longer working because your car won't meet its emissions standards and you’ll be handed a £1000 fine if you’re caught. The MoT test also checks for the presence of a DPF so if your car is supposed to have one and doesn’t, it’s an immediate fail.
Is the DPF covered under my warranty?
Your DPF is unlikely to be covered under warranty, they’re often seen as a consumable item specifically so not included. If your car’s manufacturer doesn’t specifically exclude the DPF then the company might avoid a costly warranty claim by blaming your driving style, your car's mileage or how you use it – heycar’s sister website HonestJohn.co.uk has yet to hear of a successful warranty claim for a replacement DPF.
Your car will be fitted with a DPF if it was built after 2009. DPFs burn the harmful soot produced by diesel engines and became mandatory with the introduction of Euro 5 emissions standards. That said, some older cars will also have a DPF fitted.
All new diesels have a DPF fitted. DPFs became mandatory in 2009, however, a handful of older diesels will have one fitted, too. Soot spewing out the back of your diesel is the telltale sign it doesn't have a DPF.
To stop your DPF from clogging, bring your car’s engine up to temperature and then drive it on the motorway at a steady pace allowing the engine to rev at 2000rpm or above. The heat generated will put the DPF into its regenerative cycle so that it burns off the soot it has stored.