What is a Diesel Particulate Filter (DPF)

DPFs are fitted to diesel vehicles to reduce soot emissions and have been required by law for all such vehicles since 2009. However, many vehicles were fitted with filters prior to this date, in anticipation of the incoming requirements.

Basically, they filter out most of the soot that a diesel engine creates to ensure that the vehicle complies with modern regulations, and in newer vehicles they are designed to ‘regenerate’ automatically – mainly on motorways or fast ‘A’ roads, where the high exhaust temperatures burn-off the soot that has accumulated in the filter. This is known as ‘passive regeneration’. However, if most of your motoring takes place on urban roads, or worse still, with plenty of stop/start motoring, passive regeneration is unable to create the conditions for the process to take place since exhaust temperatures will be relatively low.

In this latter case, ‘active regeneration’ is performed by the ECU (the engine management computer in your vehicle) which senses the situation and tunes the engine to increase exhaust temperatures, hence attempting to clear the filter which has become partially blocked (normally at about 45% inefficiency). If unable to clear the filter, you will now get a warning light, and if ignored, the particulates load of the filter will increase until you get other warning alarms since, in trying to clear the filter, the engine may well be running at higher that desired temperatures, and the auto regeneration cycle has a detrimental effect on engine oil viscosity and levels.

At this stage, the only answer is ‘forced regeneration’ (or, at worst, a new filter which can well cost in excess of a thousand pounds). Forced regeneration needs to be carried out at a garage that has the equipment to remove and clean the filter using specialised equipment – itself a process which is very expensive.

However, at TMVR, we have the latest state-of-the-art system that can force regenerate your filter by attaching our equipment to your vehicles throttle body and injecting steamed chemicals directly into the intake – which then cleans the combustion chamber, the primary exhaust and the filter, without removing the assembly from your vehicle. The fact that the filter can be cleaned ‘in situ’ will save you hundreds of pounds since labour costs (and time to do the job) are minimised. As part of this service we will then flush and replace the engine oil and filter, and add oil and fuel additives to ensure your vehicle and its emission systems are back to optimum condition.

It would be good to think that newer vehicles have better systems in place to ensure this problem never arises, but data from motoring organisations seems to suggest that this is not the case. Newer vehicles are just as likely to suffer this problem as their older counterparts. If your motoring is all on motorways or fast ‘A’ roads with few hold ups, your diesel engine (and its filter) should give you years of relatively trouble-free service, but should your driving be mainly in towns or country lanes and you are subject to traffic jams and stop/start motoring, a blocked DPF is very hard to avoid.

Why is this becoming more of a problem?

Years ago, one way to recognise a diesel was the clouds of black smoke (particulates) that came out of the exhaust pipe. Modern vehicles no longer do this – because of the Diesel Particulates Filter. So the result of our ever increasing air quality standards means that vehicle emissions require sophisticated systems to clean the exhaust. Standard vehicle maintenance doesn’t usually include servicing the DPF, because not all vehicles have a problem. It is not age related, or vehicle type dependant. It just depends on the sort of traffic conditions you normally encounter.

How does my vehicle know when the DPF is blocked?

Your DPF has a sensor that measures the exhaust pressure as in enters the filter, and another as it exits. In ideal conditions, with a properly clean system, this should return a figure of 0% drop off of pressure between the two sensors. Vehicles would rarely achieve this figure (except after having the filter cleaned or replaced), and are designed to cope with a blockage of about 40% – at which time the warning light will come on (vehicle dependent). However, you can continue to drive with this, but the filter will be getting increasingly blocked, causing other problems and lower fuel economy, until at some stage serious damage can be done to the engine. So never ignore the DPF warning light. Get your filter checked as soon as reasonably possible when you get to this stage.

Torbay Motor Vehicle Repairs, Unit 6 Torbay Trading Estate, New Road, Brixham, Devon TQ5 8NF

Telephone: 01803 882344.   Email: andy@tmvrbrixham.co.uk.