The DPF is a filter designed to reduce the exhaust emission, specifically soot.  This filter is a requirement for all diesel engines in order to meet the Euro 5 standard for exhaust emissions introduced in 2009.  The DPF filters all the soot in the exhaust gas to reduce the pollution. However, the filter gets clogged up with the soot and needs to be cleaned and this process is called regeneration.  Note that the life of the DPF is 5-8 years so bear this in mind if buying a second hand vehicle.

There are two types of regeneration

Active – the ECU detects when the filter is at a certain level so it increases the exhaust gas temperature to start regeneration (burning the soot away).  But it must run at a speed of at least 50mph for at least 20 minutes.

Passive – the regeneration process starts automatically when the vehicle has been running at over 50mph for 20 minutes.

Regeneration (ie cleaning of the filter) takes about 15 minutes so you must regularly drive for 30 minutes at a speed of over 50mph.

If this is not done then the DPF just gets more and more clogged and will eventually require replacement and they are expensive!

Many vehicles suffer damage to the DPF through the use of incorrect oil.  A low ash oil must be used and if it is not then the additional particles in the exhaust clog the DPF and cause irreversible damage.  The DPF has to be replaced and the cost is generally well over £1,000.

So to summarise:

  • Short journeys WILL clog up the DPF and never allow regeneration to take place
  • At least once a month (ideally weekly) the vehicle should be driven at over 50mph for at least 30 minutes (ie motorway run)
  • Always ensure you are using the exact oil as specified by the manufacturer and always a low ash variant
  • After market DPF’s rarely work so ensure you have a proper warranty (at least 12 months) and keep it safely stored in the event of failure