What is a DPF?

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A Diesel Particulate Filter (DPF) is a device which physically removes air borne particles from the exhaust gas of a diesel engine. Most of these particles are made up of carbon-based ‘soot’. Hence, DPFs are also known as ‘soot traps’. In this way, they act to reduce the harmful emissions produced by diesel engines (e.g. ‘black smoke’).


Diesel Particulate FilterOnce trapped, however, the soot will quickly build up inside the DPF if it not periodically burnt off – a process known as regeneration. This may be passive, through the use of an on-board catalyst dosed into the exhaust stream; or active, through engine management to increase exhaust gas temperature, heating the DPF, or other methods.

However, the regenerative process requires a relatively high exhaust gas temperature which is not met at slow traffic speeds – a problem if a vehicle is mostly used for urban driving. The DPF may gradually block up with soot, leading to poor running of the vehicle. In some cases a dashboard warning lamp DPF Warning Lightwill illuminate requiring immediate action which could include an expensive workshop visit and vehicle downtime. Even in the absence of actual blocking problems, fuel economy tends to worsen because the engine has to work against the back pressure caused by soot build up in the exhaust system.

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