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What Causes a Diesel Particulate Filter Blockage

What Causes a Diesel Particulate Filter Blockage?


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

This is why car makers but not the sales person often go as far as recommending city-bound short-hop drivers choose a petrol car instead of diesel (and it’s why diesels are something of a rarity in the city car sector).

Other things that are bad for DPFs include poor servicing. A diesel particulate filter on a poorly serviced car may fail sooner than a well maintained one, generally, they should last for at least 180,000 kms

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

What is a Low Emission Zone – everything you need to know a diesel particulate filter 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 freeway 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 freeway or duel carriageway road 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, 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 when the engine is turned off before the regeneration is completed.

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 10-20 minutes or so at speeds greater than 70kph

You will know whether active regeneration is taking place by 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 you may have a split intake pipe or a faulty sensor etc etc

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

We can clean blocked DPFs, without removal in a process using JLM 2 stage solution

This costs from $550 including a full diagnostic check and, while it’s not a 100% guaranteed fix, it’s successful in removing the excess soot and allowing the DPF to work and automatically regenerate again.

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 kms – again, consult your handbook for details.


Modern diesel car owners thus need to be conscious of the importance of maintaining their diesel particulate filter through driving habits and practices.

So if your having DPF or EGR issues then give us a call on 08 9309 6698 we have the perfect low cost solution on cleaning it without removal and good honest advice on how to keep it clean thereafter!

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