Back to top
Image Alt

No Salespeople Just Tradespeople

The Sound of Excellence since 1981

Diesel Particulate Filter

A common misconception is a DPF is a 4×4 issue but many diesel powered passenger vehicles are also fitted with a Diesel Particulate Filter.  Since 2016 it has been mandatory for all diesel vehicles to be fitted with a Diesel Particulate Filter (DPF) although many earlier vehicles are also fitted with them. Sadly when you are sold a car fitted with a DPF you are not really told how to look after them and that can result in some very costly repairs down the track, for you.

Those short on-off runs from home to school, to the local shops or kids’ sport on the weekend are a DPF’s worst nightmare. We’ve all seen near-new diesel 4WDs driving around city streets puffing out plumes of black smoke on acceleration, there is a good chance that black smoke is a DPF issue.

Here we explain exactly what they are, what they do, why you need them and how to look after them.  As always we are more than happy to have a look and a chat about your options or any concerns you might have.

What is a diesel particulate filter?

A diesel particulate filter (DPF) is a filter that captures and stores exhaust soot in order to reduce emissions from diesel cars. But because they only have a certain capacity, this trapped soot periodically has to be emptied or ‘burned off’, this is also known as regeneration of the DPF.


This regeneration process cleanly burns off the excess soot deposited in the filter, reducing the harmful exhaust emission and helps to prevent the tell-tale black smoke you used to see from diesel vehicles, particularly when accelerating.

Is it illegal to remove a diesel particulate filter?

Yes, it is illegal. Removing or tampering with the DPF can result in a defect notice (yellow sticker), might invalidate your insurance and/or invalidate any warranty your vehicle may still be entitled to.  There are some limitied reasons where removing a DPF is advisable but we would encourage you to discuss this with us before it’s removal.

How do I tell if my diesel particulate filter is blocked?

If the DPF is becoming clogged with soot or a fault develops in the system, an orange light will typically appear on the dashboard as seen here.


They usually look like this with a piped box that has dots in the middle, although they can slightly vary by manufacturer, it is always best to check your vehicle manual for more information.  Alternatively you are always welcome to call us for advice.

What causes a diesel particulate filter to become blocked?

Short journeys at low speeds are the prime cause of blocked diesel particulate filters.


Other things that are bad for DPFs include poor servicing and/or servicing intervals. A diesel particulate filter on a poorly serviced car may fail sooner than a well maintained one.


It’s important you use the right type of oil as well, some oils contain additives that can actually block filters.


Performance modifications can damage a diesel particulate filter, as can using low-quality fuel and even running the car frequently on a low fuel level as the car may avoid DPF regeneration in order to save fuel.

How do I maintain a diesel particulate filter?

The best way to maintain a DPF is to make sure it’s fully able to regenerate itself when it’s full of soot (when the warning light appears).


There are two types of regeneration: passive and active..


Passive regeneration

Passive regeneration occurs when the car is running at speed on long highway journeys which allows the exhaust temperature to increase to a higher level and cleanly burn off the excess soot in the filter.


So it is advised that drivers regularly give their diesel vehicle a good 30 to 50 minute run at sustained speed on a highway to help clear the filter.


However, not all drivers do this type of driving regularly, which is why manufacturers have designed an alternative form of regeneration.


Active regeneration

Active regeneration means extra fuel is injected automatically, as part of the vehicle’s ECU (computer), when a filter reaches a predetermined limit (normally about 45%) to raise the temperature of the exhaust and burn off the stored soot.


Problems can occur, however, if the journey is too short, as the regeneration process may not complete fully.


If this is the case the warning light will continue to show the filter is still partially blocked.


In which case it should be possible to complete a regeneration cycle and clear the warning light by driving for 10 minutes or so at speeds greater than 40mph.


You will know whether active regeneration is taking place by some or all of the following symptoms:

  • Engine note change
  • Cooling fans running
  • A slight increase in fuel consumption
  • Increased idle speed
  • Deactivation of automatic Stop/Start
  • A hot, acrid smell from the exhaust
What do I do if neither active nor passive regeneration work?

If your warning light continues to stay on, turns red, or additional DPF lights come on, do not leave it too long before getting it checked out.


More damage can be caused this way and what could be an inexpensive fix can become something much more expensive.


It’s a failure to correctly regenerate that is the cause of most diesel particulate filter issues: they become blocked, which increases exhaust emissions, stifles engine performance and sometimes even puts the car into a restricted ‘limp-home mode’.


On some models the engine may not restart after a number of miles – again, consult your handbook for details.


Modern diesel vehicle owners need to be conscious of the importance of maintaining their diesel particulate filter through driving habits and practices. Prevention is ALWAYS better than cure, and much cheaper.


As is always the case, if you have any concerns or are unsure what to do please call Genie Exhaust.

contact us

(08) 9330 6900
30 Shields Cres., Booragoon WA 6154
  • This field is for validation purposes and should be left unchanged.