Diesel Particulate Filter


Diesel Particulate Filter

Unlike the DOC, the diesel particulate filter (DPF) is a wall-flow filter consisting of a matrix of materials (a composite of cordierite, silicon carbide, or metal fibres) that traps any remaining soot that the DOC couldn’t oxidize. Wall-flow diesel particulate filters usually remove 85% or more of the soot, and under certain conditions can achieve soot removal efficiencies approaching 100%. Some filters are a single-use unit, intended for disposal and replacement once full of accumulated ash. The soot remains in the DPF until it is regenerated either passively, actively or forced.

Diesel particulate filter for heavy-duty vehicle (a), cross-section viewing showing filtration processes within several DPF channels (b), and close-up view of particle capture and build-up on the channel walls (c).

Passive regeneration occurs during the vehicle’s normal operating temperatures when engine load and vehicle drive-cycle create temperatures that are high enough to regenerate the soot build up on the DPF walls. The DPF will oxidise the particulates anywhere between 275-360⁰ Celsius. Passive regeneration takes place automatically approximately every 400-800 km depending on the quantity of particulate inside the filter and the driving behaviour.

Active regeneration happens while the vehicle is in use, when low engine load and lower exhaust gas temperatures inhibit a passive regeneration. Sensors upstream and downstream of the DPF (or a pressure differential sensor) provide readings that initiate a measured addition of fuel into the exhaust stream. There are two methods to inject the extra fuel, either downstream injection directly into the exhaust stream, downstream of the turbo, or fuel injected into the engine cylinders on the exhaust stroke. This fuel and exhaust gas mixture passes through the Diesel Oxidising Catalyst (DOC) creating temperatures over 600 degrees Celsius to burn off the accumulated soot. Once the pressure drop across the DPF lowers to a calculated value, the process ends, until the soot accumulation builds up again

This regeneration process occurs at road speeds higher than can generally be attained on city streets. Vehicles driven exclusively at low speeds in urban or peak hour traffic can require periodic trips at higher speeds to trigger an active regeneration to clean out the DPF. If you as a driver ignore the warning light and wait too long to operate the vehicle at about 100km/hr for a reasonable time frame the DPF may not regenerate properly and continued operation past that point may cause damage to the DPF filter resulting in the need for a complete replacement.

Pressure drop evolution with soot accumulation in the DPF showing rapid initial rise in pressure drop due to soot accumulation in the filter pores (1) followed by a gradual increase as soot builds a layer along the walls (2).

If the DPF develops too much pressure then the last type of regeneration must be used - a forced regeneration. This can be accomplished in two ways.

  • 1. The Vehicle operator can initiate the regeneration via a dashboard mounted switch. Various signal interlocks, such as park brake applied, transmission in neutral, engine coolant temperature, and an absence of engine related fault codes are required (vary by OEM and application) for this process to initiate.
  • 2. When the soot accumulation reaches a level that is potentially damaging to the engine or the exhaust system, the solution involves a qualified technician using a computer program to run a regeneration of the DPF manually.

Back pressure usually returns to normal after the soot is oxidised during an active, passive or forced regen, however don’t forget about the remaining ash! It builds up inside the DPF and does not burn or oxidize like soot and will remain in the DPF until removed.

Ash is made of minerals, metals and other trace elements from the breakdown of lubricants, additives and engine wear.

Ash builds up at a much slower rate than soot but if it’s ignored will eventually cause an increase in back pressure, fuel consumption and at worst DPF failure. As the ash builds up inside the DPF the number of active regenerations increase causing fuel economy to become poor, temperatures inside the DPF to become extreme which can severely damage the construction of the internal filter system and more constant back pressure that can be detrimental to the turbo itself.

The longer the ash is left inside the DPF the higher the chance of it hardening into a plug which closes off that portion of the filter.

Shorter intervals between regenerations is the first clue to ash build up and is a tell tale sign the DPF needs to be removed for cleaning. This can also be observed by logging the regen cycles in a workshop with diagnostic equipment. When the DPF is removed for cleaning it’s always a good practice to also remove the DOC and clean it as well if necessary.

Failure of fuel injectors or turbochargers resulting in contamination of the filter with raw diesel, engine oil or debris can also necessitate cleaning.


As an owner/driver of a Diesel powered vehicle you need to clean the DPF regularly as this will save you money in operating costs and prevent costly downtime in the long run.

Maintenance schedules or cleaning cycles vary according to the type of vehicle and how your vehicle is being used.

To keep your DPF’s optimal operating performance we suggest a clean at least every 12 months. Shorter timeframes may be needed if your vehicle is exposed to:

  • peak hour traffic at low speeds
  • numerous short stop/start trips (less than 20 minute trips)
  • extended periods where engine is at idle

For vehicles that operate on the highway at least once a week or more for periods of at least 30 minutes at a time, we recommend a full DPF service and clean every 100,000km providing the below issues have not affected the operation of the DPF.

  • Poor fuel consumption
  • Noticeable decline in performance
  • DPF light keeps illuminating on the dash at shorter and shorter intervals
  • Vehicle goes into limp mode after DPF dash light comes on
  • If your vehicle has had a failure with fuel injectors, turbo, head gasket, high oil consumption, EGR system malfunction/failure
  • Increase in smoke from exhaust system

Exhaust Clean Australia guarantees the fastest turnaround times in the market due to our revolutionary Flash Clean technology. This patented Italian made machine is the best of the best, guaranteeing the fastest clean and the very best results or your money back.

We can pick-up from your workshop, and deliver your DPF back in as little as 3 hours. We offer a range of services, including:

  • Priority Service (next in line)
  • Same day service
  • Standby budget service

If your DPF is oil soaked due to an engine component failure allow extra time for an additional step in the cleaning process to return your DPF back to its original state.

Exhaust Clean Australia offer warranty on all our workmanship where the vehicle is operated according to manufacturer’s specification.

Pricing structure here:

From as little as $ 350. Compare that the cost of a replacement DPF that could set you back anywhere from $1,500 - $15,000 for cars, and in excess of $25,000 for large trucks and machinery. Cleaning your DPF is a very cheap cost alternative for your car, truck or machine.

  • Diesel particulate filters – from $450 + gst
  • Cat Convertors – from $340 + gst
  • Diesel oxidising catalysts – from $340 + gst
  • Selective catalyst reductors – from $390 + gst
  • Intercoolers – from $110 + gst
  • Exhaust gas recirculation – from $100 + gst

There are some chemical fuel additives on the market that claim to be able to clean blocked DPF’s but do not remove ash build up. They are extremely ineffective and a waste of your hard-earned money. Some additives may remove some soot from the filter walls but there is a large amount of chemical residue retained in the DPF itself which is absorbed by the remaining ash content. This residue contributes to future blockages occurring in a much shorter time frame.

To help prevent your DPF from blocking up again try to drive the vehicle at least once a week on the highway for 30 minutes or more. This will ensure that the DPF will perform a passive regeneration (self-activated) and the soot gets cleaned from your DPF. Ensure that the vehicle’s service schedule is adhered to and correct engine oil is used. Find an independent mechanic that is familiar with your make and model of vehicle and is experienced in servicing modern diesels. This will ensure that they have a thorough knowledge of your vehicle and will know all the tips and tricks in fault finding any problems.

DPF systems are very technical and some mechanics may not fully understand their complex operation, and in our experience that also includes some dealerships. Some workshops may use the “keep replacing parts” method hoping it’ll solve the fault, but inevitably your bank balance will cop a hiding! Try to find a diesel specialist workshop that frequently deal with DPF systems and understand how they work. They’ll be able to pinpoint the cause of the fault and only replace or repair the parts that are necessary.

Exhaust Clean Australia can provide a removal and refit service of your DPF at our workshop for all vehicles sizes. We can also provide a list of recommended mechanics in your area that can perform the removal and fitting service for you, while ensuring that your DPF is still being cleaned by the best in the business.

No, it’s illegal to remove or delete your DPF. Your vehicle has been designed by the manufacturer to operate with a DPF system. It is illegal and will also void the manufacturer’s warranty on your vehicle and Australian consumer law protections. Removal or deletion of your DPF will also impact your vehicle’s insurance policy due to fire risk.

DPFs are fitted to enable the vehicle to comply with the Australian Design Rules (ADR) emission requirement levels.

The relevant ADR for light vehicles is ADR79/01

The relevant ADR for heavy vehicles is ADR80/01

It is illegal to operate a vehicle that does not meet the ADR requirements so removing or deleting a DPF will result in non-compliance with all relevant emissions ADR’s.

In addition to commonwealth legislation, each state and territory also have additional legislation that require DPFs to be fitted and operated in accordance with manufacturer requirements.

Don’t be fooled by dodgy operators that claim to electronically delete your DPF without detection. Authorities are now cracking down on engine tuning shops and vehicle owners who employ this practice, using sophisticated tools to identify vehicles suspected of having no DPF or deleted DPF. Stiff prison sentences are now being applied for this practice, with numerous prison sentences already handed down.

Download our troubleshooting checklist to assist your mechanic in diagnosing the cause of your DPF malfunction.

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