What is a Diesel Particulate Filter?
Most modern diesel vehicles are fitted with a Diesel Particulate Filter (DPF) which removes harmful soot from the exhaust gases before they enter the atmosphere.
Why have a DPF?
In order to meet strict European emissions legislation, DPF’s are used to help reduce the amount of pollutants from diesel engine vehicles.
Using advanced technologies, the DPF reduces exhaust smoke and black soot, significantly lowering emissions and protecting the environment.
How does the DPF work?
As well as converting harmful exhaust gases in the same way as a conventional catalytic converter, the DPF also ‘traps’ soot particles (particulates) that are produced in the exhaust gas. The DPF continues to do this until a predetermined level is reached.
As with any filter they have to be emptied regularly to maintain performance. For a DPF this process is called ‘regeneration’ – the collected soot is burnt off at high temperature to leave only a tiny ash residue.
Symptoms of active regeneration
During active regeneration you may notice the following symptoms:
– Cooling fans running
– Increased idle speed
– Deactivation of automatic Stop/Start
– A slight increase in fuel consumption
– A hot, acrid smell from the exhaust.
– Engine note change
How will the DPF affect me?
In order to carry out the regeneration, the DPF needs to reach and maintain a higher exhaust temperature than normal. Under most conditions, your car can do this unaided.
However, in some circumstances, it can’t reach the required temperature (usually due to frequent short journeys or stop-start driving), in which case the driver is normally alerted by a warning light and/or a message appearing in the instrument panel, depending on the make and model of the vehicle.
What should I do if the warning light comes on?
Most importantly, do not ignore it. If the light has come on, it does not necessarily mean there is a fault with the DPF. It’s simply telling you that the Diesel Particulate Filter on your car needs help in carrying out the DPF Regeneration.
To do this, you need to drive in a particular way to increase the exhaust temperature – typically 10-15 minutes at a suitable road speed, whilst maintaining an engine speed of approximately 2,500rpm. (This may vary depending on make and model of vehicle).
If you fail to address the issue, the DPF light stay on and additional lights or symbols may also come on as soot levels will continue to increase. Check your vehicle handbook for details.
You may also experience a reduction in power, followed by a complete DPF blockage and the need for a costly replacement filter.
What happens if two or more lights come on?
If more lights come on, the DPF Regeneration can usually only be carried out at an authorised repairer and should be done immediately.
Apart from a reduction in engine power, the engine may fail to start if ignored.
Is there anything else I should know?
If the DPF needs replacing as a result of ignoring the warning lights or messages, the cost of replacing the DPF may not be covered by the manufacturer’s warranty, if still in force.
Note, if your car is fitted with a DPF, you should not use 100% RME (rapeseed methyl ester) biodiesel as this can cause damage to the fuel system.
Use forecourt BS EN 590 diesel only.
From February 2014 the inspection of the exhaust system carried out during the MOT test will include a check for the presence of a DPF. A missing DPF, where one was fitted when the vehicle was built, will result in an MOT failure.