DPF stands for diesel particulate filter. These filters reduce the number of hazardous particulates that escape the engine exhausts of diesel engines. The goal is to keep the air cleaner and safer, particularly in tight spaces. Keep reading to learn more.

Euro 5 standards

Since 2009 when the “Euro 5′ standard came into effect, exhaust emissions standards for diesel vehicles of the new generation have required the fitting of the DPF into the exhaust system. In actuality, the majority of vehicles that were built before 2009 will come with an exhaust filter installed as well.

These measures are taken for good reason because DPF (soot) emissions cause serious health problems in humans. DPFs lower the emission of diesel smoke by 80% however they’re not suitable for everyone. Even if your driving style is not typically urban or stop-start-type, modifications to your driving habits may be required to ensure these systems function efficiently.

What is the process by which diesel particulate filters function?

Diesel Particulate Filters (DPF) filter out soot particles, which prevent them from going through the exhaust. Just like any other filter, they must be emptied regularly to maintain performance. For the case of a DPF this process is called “regeneration”. The collected soot is burnt off by high temperatures so that there is only ash.

Regeneration can be either passive or active

Passive regeneration

Passive regeneration takes place automatically at the speed of the motorway when the exhaust temperature is high. Because a large portion of vehicles isn’t driven on the motorway very often, vehicle manufacturers have created “active” regeneration. In this case, engine management computers (ECU) take control of the process.

Active regeneration

If the filter is filled up with soot to a certain amount (about 45%) your vehicle’s ECU will start post combustion fuel injection to raise the temperature of exhaust and trigger regeneration. If the motor is shut off while regeneration is being completed, it could not be finished, and the warning light comes out to indicate that the filter is blocked partially.

It should be possible to complete a regeneration cycle and then clear the warning light by driving and increasing the temperature that way.

The symptoms of active renewal

During active regeneration, you might notice these symptoms:

  • Cooling fans running
  • Increased idle speed
  • The deactivation of automatic Stop/Start
  • A slight increase in fuel consumption
  • A strong, spicy smell from the exhaust.
  • Change to note on engine

If the regeneration fails because of a lack of drive cycle, the extra fuel injected into the cylinders won’t burn and will drain to the sump. Therefore, the quality of the oil will decline and the oil level will increase. Many DPF-equipped vehicles will include an oil quality/viscosity monitor, however, it is crucial to verify that the oil’s level does not increase above what is the maximum value on the dipstick as diesel engines can run on their own oil if the level is too high – often to the point where it threatens destruction.

If you fail to notice the diesel particulate filter warning light and continue driving at a moderately slow with a stop and start pattern, soot can increase until around 75% when you’ll likely notice additional dashboard warning lights turn on. At this point, driving at a high speed will not suffice to eliminate the filter. You’ll need to take the car to a service center to get “forced” regeneration.

Forced regeneration

Regeneration by force is mandatory when “active” regeneration criteria have not been achieved and the soot levels in the DPF have increased to about 70%. If left unattended, the load of soot continues to build up. At this point, a diagnostic tool must be used to force regeneration. Around 85% of soot load, regeneration can no longer be done on the vehicle. In this case, you will need to get rid of your DPF to be cleaned or replaced.