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All you need to know about Diesel Particulate Filters

At Cavendish Motor Company we’re keen to ensure you have trouble free motoring in a car you can trust. We receive a fair number of enquiries for DPF faults so thought it’d be a good idea to give you the information you need to keep yours healthy.

What is a DPF?

Diesel Particulate Filters (DPFs) are fitted to modern diesel cars to reduce pollution but if they block up they can cause very expensive problems.

It’s a given that diesel engines produce a lot of soot or particulates. These can cause respiratory problems and increase the risk of heart disease.

Since 2009 diesel cars that come off the production line must be fitted with an exhaust with a  DPF to prevent this soot entering the atmosphere.

The aim according to the Euro legislation is to cut 80% of particle emissions. However, this DPF technology has problems and garages often have to deal with cars that have blocked DPFs.

In order for the car’s performance to be maintained it’s important that its DPF is emptied regularly. The process is called ‘regeneration’ and is normally carried out passively, that is when the exhaust temperature is high enough, which usually requires cars to be driven on smooth running roads like motorways or fast A-roads.

What happens is that the soot is burned off, and only a small ash residue is left. It’s not possible to remove this ash unless the DPF is dismantled and sent for specialist cleaning. But it should not matter as a car fitted with a DPF and used in the correct manner should be OK for much more than 100,000 miles.

 

Common Causes of Failure?

A lot of cars that are used mainly in towns and don’t, therefore, benefit from being driven on the open road so they can perform passive regeneration are fitted with ‘active’ regeneration systems. These allow the engine to control the regeneration process with software that monitors the DPF becoming blocked when it injects extra fuel to increase the exhaust gasses temperature and trigger the necessary regeneration.

This active regeneration should be initiated every 300 miles or so depending on how the car is driven and takes between 5 and 10 minutes to finish. However, when your journeys are too short the regeneration can’t complete.

In these circumstances you may well detect:

  • The cooling fans will come on
  • A faster engine idling speed
  • The automatic Stop/Start mechanism no longer works
  • Fuel consumption increases
  • There is an acrid smell
  • The engine sounds odd

 

 

If this happens don’t ignore any warning light. It may indicate the filter is blocked, so you should complete the active regeneration process by taking the car for a drive of more than 15 minutes at over 40 mph.  You’ll find the specific instructions for your vehicle in the driver’s handbook.

Don’t ignore the DPF warning light and continue to drive in a relatively slow, halting pattern. It will cause a soot build-up that eventually triggers your car’s ‘limp home mode’ in a bid to prevent additional damage.

If this happens you will need to get a garage to carry out a manual filter regeneration. The garage may replace the filter, which can cost over £1,000 plus labour. In the majority of cases, it’s only a  short period between the DPF becoming partially blocked and it needing an emergency manual regeneration.

 

Why is a DPF required?

To meet European emissions regulations DPFs have to be fitted to modern diesel cars. It is an offence to drive a car that has been modified so it no longer complies with the prescribed emissions standards. Removing a DPF can also invalidate your insurance cover.

Since February 2014 any car that had a DPF fitted during construction will fail its MOT if the DPF has been removed or modified.

 

How To Avoid A Big Bill?

So… if your DPF light is on and remains lit after you’ve followed the instructions in your handbook for regeneration (driving on a dual carriageway etc), what next?

We’re keen to keep any remedial work to a minimum which is why accurate diagnosis is essential.  There are a number of subsystems that are required for efficient regeneration (glow plugs, additive injectors etc), it’s very common for one of these to have caused the fault.Once we’ve found the root cause we can then assess if cleaning the DPF is suitable.

At Cavendish Motor Company we have a lot of experience in DPF repairs. You’ll be guaranteed a high level of workmanship and great value.

Call today with you DPF faults. We’re here to help.