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The Motorists' Guide

Guide to Diesel Particulate Filters (DPF)

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Steve takes a look at Diesel Particulate Filters. 

Diesel Particulate Filters or DPF for short has become a dreaded talking point for diesel car owners in recent years, so what are they, how do they go wrong, and how can you prevent your DPF from failing. 

What is a Diesel Particulate Filter (DPF)?

The DPF can be found on vehicles made from 2009 onwards which come under Euro 5 emissions standards. Its purpose is to reduce soot deposits from entering the atmosphere from the cars exhaust system. The DPF collects the soot within the filter and when it is at least 45% full the car will automatically carry out what is known as a regeneration of the DPF. The regeneration uses the heat from the engine/exhaust system to burn the soot, thus preventing it from entering the atmosphere. You will know when a regeneration is taking place as you may experience a higher idling speed, vehicle fans running, lower MPG or a burning smell from the exhaust. 

Where can I find the DPF?

The DPF is located underneath the car on the exhaust system and looks like a cannister as per the picture below. 

Does it go wrong? 

The DPF can become clogged with soot and eventually stops working. this is often caused by the car not being used for long journeys which allow the engine to get up to full operating temperature, such as only being used for town driving only or short commutes of 10 miles or less. It is therefore important that a diesel car gets a good motorway run at least once a week to allow the engine to get to operating temperature so it can carry out a DPF regeneration. if the DPF has become blocked your car may develop a loss of power or go into limp mode as well as an engine management light illuminating on the dash. Picture below shows what the DPF light on most vehicles looks like. 

Can it be cleaned? 

yes it can and can be done in four ways, firstly by giving your car a good motorway run at least once a week for 30 minutes making sure it reaches full operating temperature. This form of regeneration is known as a passive regeneration. However your vehicle may do an active regeneration which involves the car pumping fuel into the engine thus increasing the heat of the exhaust and ultimately burning off the soot.  Secondly, running DPF cleaning additives in your fuel to help keep it clear. The third way is getting a mobile DPF cleaning specialist to come and do a forced regeneration and clean of the DPF. The forth way is more time consuming and requires the DPF to be dismantled and physically cleaned. 

Is it easy to replace? 

The replacement of a DPF is a time consuming job but can be done by an experienced DIYer. Alternatively a garage can replace your DPF but be warned, the bills can run well over £1000 dependent on manufacturer.  Also be aware that removing the DPF completely is illegal and fines can be upto £1000, plus it will void your insurance/MOT. 

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