What is a DPF - Diesel Particulate Filter?

A diesel particulate filter collects the soot produced by the exhaust gas in a diesel engine. It is held there until it the engine reaches temperature and then burnt off so as to help reduce the gas emissions.

How does a DPF work?

The diesel particulate filter works by burning off soot once it reaches a certain temperature through regeneration. There are 2 different types of regeneration methods.

Passive Regeneration

This takes place automatically and you do not get alerted to this. To get the filter trap hot enough to self regenerate, you need to keep the vehicle running for at least 20-30 minutes at a reasonable speed - above 60kmh. This needs to be done once every full fuel tank of diesel. Stop-start driving or around city trips may not allow the exhaust to get to temperature to carry out this regeneration. If this doens't work, the vehicle will move onto Active Regeneration

Active Regeneration

The Engine Control Unit (ECU) will read the levels of soot in the DPF. If the vehicle is not performing a passive regeneration long enough, the soot levels may rise and once it gets to approx 45% the ECU will perform an active regeneration. This is where a small injection of diesel fuel is pushed into the engine after main combustion cycle to increase the temperature of the exhaust and to trigger the passive regeneration. You will normally see the DPF light pop up on the dashboard to let the driver know this is in process. If this process is interupted or can't be completed for any number of reasons, the car will go into limp mode.

Is a Forced Regeneration good for the filter or the engine?

Depends on the soot and ash levels in the DPF. If they are too high and the temperature rises too high, this can cause the debris to expand fracturing the ceramic and damaging the particulate filter. The only way to know the soot levels is to get the filter inspected by a professional, like the ones at Dufty Automotive Services.

Forced Regeneration

A forced regeneration is done when the vehicle is no longer regenerating on its own. This should be done by a mechanic with experience. If the soot level is too high for the ECU to do a passive or active regeneration, then a diagnostic scan tool is used to override the soot levels calculated by the ECU. This then forces the vehicle to do an active regeneration to burn off the soot.

When would I need a new filter ?

The lifespan of a DPF is dependant on many factors and it is hard to determine when a filter requires replacement. It is common for a DPF to be replaced once a car has driven any where between 120,000 - 200,000kms with that filter, however this is dependant on the cars usage. If the DPF is so blocked that it cannot be regenerated, it may need a manual clean by a technician.

How to prevent a DPF replacement

To prevent DPF failure, it is important to adhere to the maintenance schedule provided by the manufacturer. This includes regular replacement of the oil and air filters, as well as the use of the appropriate fuel and oil types. It is also important to ensure that the engine operates at the optimal temperature for regeneration. In order to minimise the risk of DPF failure, it is recommended to avoid short journeys or stop-start driving whenever possible. In case short journeys are necessary, it is advisable to take the vehicle for occasional longer drives at higher speeds to help with DPF regeneration.