DPF stands for diesel particulate filter. These filters help reduce the number of hazardous particulates that get into the engine exhausts of diesel vehicles. The intention of DPF filter is to help make surrounding air healthier and more secure, particularly in small spaces.
Euro 5 standards
Since 2009, when the “Euro 5′ standard was put into force, the exhaust emissions standards for diesel vehicles of the new generation have required the fitting of a DPF for the exhaust system. Indeed, a lot of cars that were registered prior to 2009 will have filters fitted too.
The measures are well-intentioned since diesel particulate (soot) emissions cause serious health problems in humans. DPFs reduce the emissions of diesel soot by 80%, but they’re not for everyone. Even if you drive not typically urban or stop-start-type, modifications to your driving style could be required in order to keep these systems operating effectively.
How do diesel particulate filtering systems work?
Diesel Particulate Filters (DPF) catch soot particles to avoid them exiting out of the exhaust. Like any filter that is used, they need to be cleaned frequently to ensure their performance. For a DPF this is known as “regeneration”. This process involves the collected soot being burned off at a high temperature and leaving only ash.
Regeneration can be active or passive
Passive regeneration
Passive regeneration is a process that occurs automatically on the motorway if the exhaust temperature is very high. Since a lot of cars aren’t used on motorways often, manufacturers of vehicles have designed “active” regeneration. In this manner, the engine management computer (ECU) controls the process.
Active regeneration
If the filter is filled with soot to an amount that is set (about around 45%) then the car’s ECU will trigger post-combustion fuel infusion to increase the exhaust temperature and initiate regeneration. If the motor is turned off while regeneration is in progress, it may not complete and the warning light comes out to indicate that the filter is not fully blocked.
It should be possible to complete a cycle of regeneration and also clear the warning lights by driving and increasing the temperature.
The signs of active regeneration
In active regeneration, you may have the following symptoms
- Cooling fans running
- Increased idle speed
- Deactivation of the automatic Stop/Start
- A slight increase in fuel consumption
- The smell is hot and acrid emanating from the exhaust.
- Engine note change
If the regeneration is unsuccessful because of an insufficient running cycle, the extra fuel that is injected into the cylinders will not be burned and will flow into the sump. This means that the quality of the oil will decrease and the level of oil will rise. Many DPF-equipped vehicles will include an oil quality/viscosity monitor, however, it’s important to ensure that the oil level is not higher than what is the maximum value on the dipstick because diesel engines are able to run on their own oil when the level is high, often to the point of destruction.
If you fail to notice the diesel particulate filter warning light and drive with a comparatively slow with a stop and start pattern, soot can continue to build up until around 75% when you’ll likely notice additional dashboard warning light lights come on. At this point, driving at speed alone will not be enough to completely clear the filter, and you’ll have to take your car to a mechanic for “forced” regeneration.
Forced regeneration
Forced regeneration is needed when “active” regeneration criteria have not been met and the soot levels within the DPF are now at around 70%. If left unattended, the load of soot will continue. At this level, the diagnostic tool should be utilized to trigger regeneration. At around 85% load, regeneration can no longer be achieved on the vehicle. You will need to remove it from the DPF to be replaced or cleaned.