The original article detailing my experiences with the DPF (Diesel particulate filter) in my 2008 Nissan Qashqai 2.0Dci has proved to be very popular by people also experiencing issues.
In order to help my fellow diesel DPF users, we have put together a page dedicated to this small “environmentally friendly” and costly device.
What is a DPF?
A diesel particulate filter (DPF) is a device which sits in the exhaust system, it “captures” soot / diesel particulate and other nasty particles so they are not released into atmosphere. A diesel particulate filter can remove upwards of 85% of the particles from the exhaust, reducing harmful emissions.
The DPF physically captures the soot and ash particles in a net or mesh like structure within the filter.
Does my vehicle have a DPF fitted?
UK emissions standards for cars effectively required fitment of a DPF in the exhaust of diesel cars in 2009 when the ‘Euro 5′ standard came into force. Many cars before this time already had one fitted in anticipation of this requirement but its generally accepted that very few diesel cars manufactured before 2006 had a diesel particulate filter fitted.
If you are in any doubt, the unit should be visible if you have under the vehicle. They are normally located to the front of the exhaust system. If you’re not mechanically minded then it may be beneficial to take along a mechanic if you are looking to buy a car but are keen to avoid having a DPF.
What does the DPF warning light on my dash mean?
The DPF warning light displayed on the dash board indicates that the filter is not working correctly or is in need of maintenance / regeneration. Sensors within the device or the exhaust monitor the back pressure and temperature of the system to ensure its working correctly. When the readings from this sensors are outside a preprogrammed limit this will trigger the warning.
Once activated, the light should trigger a regeneration of the filter or could indicate that the device is faulty and in need of replacement or repair.
DPF regeneration / cleaning
There are two different types of DPF regeneration that are commonly used. These are active and passive. Which ever your car uses you’ll still have to meet some strict conditions in order for the regeneration to start. It’s usually a combination of engine temperature, speed and RPM. A rule of thumb is that the engine needs to have reached normal operating temperature, you’re travelling at more than 40MPH and the RPM (revs) of your engine is at least 2500 RPM. Depending on how blocked or effective your regeneration will determine how long it needs to be performed.
DPF Regen Conditions
- Engine at normal operating temperature
- At least 40MPH
- At least 2500RPM
- Fingers crossed!
Below is an explanation of the different types of regeneration.
Active regeneration of the DPF is performed by the ECU triggering a post combustion fuel injection. This increases the temperature in DPF, burning off the soot and particles that build up in the filter. This type of regeneration can cause higher than normal fuel usage.
Passive DPF regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. Many manufacturers have moved to using active regeneration as many motorists do not often drive prolonged distances at motorway speeds. Passive regeneration often uses a DPF additive (see below).
Forced regeneration is a way of cleaning the DPF using a maintenance process which has been built in by the vehicle manufacturer. This process can only be started by either a main dealer / mechanic with the right tools and access to the vehicles management systems. This process usually involves kicking off a DPF clean cycle in the workshop which runs the car at a high RPM for a considerable period of time. The ECU ensures that this cycle heats up the DPF filter to an extreme temperature, burning off the contents of the filter. It some cases the ECU injects fuel into the post combustion process to achieve these temperatures. In most cases the engine oil will need to be changed as the vehicle will literally “cook” the lubricant.
DPF cleaning is a manual process that removes the soot and diesel particulates from the filter. DPF cleaning is achieved using by utilising ultrasonic cleaning technology in combination with specialist chemicals. This process removes all traces of particulate, returning it back to near new condition.
There are many companies in the UK offering DPF cleaning services with many offering a guarantee period, free collection and return. Having your DPF cleaned in this way is certainly a viable alternative to replacing the entire unit considering what it would cost to replace it.
Click for more on DPF Cleaning
DPF Cleaners At Amazon
What is a DPF additive?
Some manufactures utilise a DPF additive which is automatically added to the fuel. This additive is used to increase the chance of a successful regeneration. The additive allows the soot and ash to be “burnt” at a much lower temperature than that required during an active regeneration. The additive is usually replenished during servicing as part of manufactures guidelines.
There are a number “over the counter” DPF additives which can bee added to your fuel tank. These too claim to help reduce the temperature which soot will burn. Read more about how these work here DPF Cleaning
Why are diesel particulate filters so expensive?
DPF filters contain a fine mesh light structure that acts like a net. This net captures the soot and diesel particulates, stopping them from being released into the air. Modern DPF filters are made from various materials such as a matrix of porous ceramic material, Silicon carbide or metal fibers. Due to the materials used and complex design of the structure the filter can often cost upwards of £1000.
How long should a DPF last?
The lifespan of a DPF is very hard to determine. There are many factors to take into account however we would hedge our bets on expecting a DPF for the average motorist to last in excess of 70k miles from new. For the occasional city driver this maybe considerably sooner due to increased soot levels and the ability for the DPF to regenerate under normal driving conditions.
Can I clean my DPF? Should I use a DPF cleaning fuel additive?
Do no believe what it says on the tin or what you read on website selling “snake oil. Read more here for further information on cleaning your DPF filter.
What should I do when I see the DPF warning light?
In the first instance we would suggest that you contact your manufacturer service centre for advice when the DPF warning light is displayed. Depending on the model and make of your car, the process of regenerating the filter will differ. If you are still unsure how best to clear the DPF then we would advise seeking advice on the vast array of owners club message boards and forums.
Failure to correctly regenerate the filter in a timely manner can lead to a costly manual regeneration or in the worst case – failure of the device. See the section above for information on how regeneration takes place however we would strongly suggest that you speak to a mechanic before wasting time and fuel.
My car has a DPF cleaning button. What the hell is it and how do I use it?
Some vehicles such as trucks or 4x4s are not able to meet the conditions required for an “automatic” DPF regen. They are often fitted with a DPF cleaning button – we’ve dedicated a page to this very topic. Click to find out more about DPF Cleaning Button Switch
My car has an automatic gearbox, how to trigger a DPF regeneration?
If you have an “auto” box and need to perform a DPF regeneration it could a little tricky to get the revs high enough for a regen without breaking the speed limit. Truy using the SPORT / S mode setting on your transmission to force the car to hold the revs higher without changing gear. It may take a little time to work out the sweet spot for the change but at least it’ll help you keep those points off your license.
My Mercedes C class is one of the increasing number of cars that feature a manual mode with flappy paddles that make you think you’re some kind of racing driver. This mode allows you to keep the revs much her in gear and hold them there. Depending on the car it may trigger a kick down if you push the accelerator all the way down to the floor.
Now the DPF warning light and Check Engine / Management (engine warning lights) are on!
With most vehicles the DPF warning light will illuminate to notify you that the unit is becoming blocked and requires regeneration. When the car meets it’s conditions for a regeneration it will attempt to burn off the built up soot using either an active or passive regeneration. If the regeneration is unable to occur or fails you may be treated to an additional light on your dash in the form of an Engine Management Light or Check Engine Light. This usually occurs when the car is beyond the point at which a normally regeneration may occurs and indicates a dealer / garage visit is in order.
When the EML / CEL appears your car may go into limp home mode. This may restrict engine power and revs, resulting in additional misery!
I have a DPF, what engine oil should I use?
Always use the manufacturer approved engine oil if you have a DPF. Most manufacturers specify a low SAPS oils. Low SAPS oils are specifically designed to be low in Sulphated Ash – a by-product of diesel combustion that causes the DPF “mesh” to become be blocked. It’s also advised to ensure your oil is changed well within recommended manufacturer guidelines.
What can cause my DPF to block?
Faulty / Damaged EGR Valve
It’s not just your driving habbits that can cause your DPF to block. There is another little gremlin sitting under your bonnet that could be the cause of all your DPF woes… your EGR valve.
An EGR Valve is a small engine component that recirculates a portion of your exhaust gases back into the engine. This process is primarily aimed at reducing the levels of nitrous oxide (NOx) being emitted through the exhaust system.
Over time EGR valves can become blocked with the soot and carbon it is designed to recirculate, this in turn can cause the device to stick open or open for longer than it should.
A faulty EGR valve that is stuck open will increase the amount of particulates, soot and carbon to to be fed back into the engine, in turn increasing particulates produced by the engine and causing your DPF to become blocked much quicker than expected.
A faulty EGR valve will often cause an error code in the ECU and may also cause the car to idle roughly. We’d recommend having your EGR checked if you are experiencing recurring DPF regeneration or frequent DPF warning lights.
Can I remove my DPF?
Due to the high costs of replacing diesel particulate filters, a whole industry has emerged around removing the devices completely (DPF removal). This involves replacing the unit with a pass through pipe or modifying the existing unit and removing the mesh or filters inside.
The removal of the DPF will cause the ECU error and therefore the service will most likely also include the removal of the error and associated programming from the ECU software.
The marketing of this services often includes claims of reduced running costs, extra power and increased efficiency.
Is is legal to remove my DPF?
According to the DPF guidance sheet on the .GOV website. Its is an offence to remove the DPF filter.
It is an offence under the Road vehicles (Construction and Use) Regulations (Regulation 61a(3))1 to use a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet. Removal of a DPF will almost invariably contravene these requirements, making the vehicle illegal for road use.
A vehicle might still pass the MoT visible smoke emissions test, which is primarily intended to identify vehicles that are in a very poor state of repair, whilst emitting illegal and harmful levels of fine exhaust particulate.
With this is mind PLEASE we strongly advise you check out our article regarding DPF filter removal and your MOT
Is my DPF filter covered under warranty?
The DPF is seen as a consumable by many manufacturers and warranty providers. The cost of replacing or regenerating the filter is normally not covered but we would suggest seeking advice if you are experiencing DPF related issues.
I’m constantly having issues with my DPF, what next?!
If your driving habits are not sutable for DPF equipt car, you have a defective DPF or regeneration issue we strongly suggest you do what I did. Sell it and move on. Petrol cars DO NOT HAVE DPF FILTERS!
Check out our top DPF tips for keeping your DPF clean
Check out our top 5 tips on keeping your DPF clean and trouble free. Click for our top 5 DPF tips
We hope you found this article useful and we would appreciate your feedback / requests for additional information. Please share using the buttons below and feel free to contact us to help us offer even more useful information.
We need your help!
If you’ve been confronted with DPF issues and you’ve managed to fix them yourself then please let us know in the comments below. It might just help a fellow motorist escape the expense of a dealer regen or a replacement filter.
For more information on DPFs you might also like to check out the following pages
- The Diesel particulate filter (DPF) FAQ
- The Exhaust Gas Recirculation Valve EGR FAQ
- Our top five tips on keeping your DPF clean
- Diesel remap & tuning boxes will my diesel particulate filter DPF cope?
- DPF Cleaning specialists reveal top 10 vehicles with DPF issues
- Which cars have the most DPF problems?
- Skoda Octavia iii 2013 Diesel Particulate Filter DPF – Owner’s Manual – Regeneration FAQ
- Hypermiling Top Tips: Top 5 causes of blocked / Failed DPF diesel particulate filters