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All you need to know about Diesel Particulate Filters

At Saffron Autos 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.

Diesel Particulate Filters are fitted to all diesel cars built after 2009. The reason is to help them get through increasingly tight emissions control tests that have been imposed by Euro regulations.

You may not know you have one, but if a problem with the DPF ever occurs you will find yourself facing a large bill for engine repairs.

What is a DPF?

What a DPF does is effectively trap soot. By filtering and storing the exhaust’s soot the DPF helps cut emissions and prevents the billowing black smoke that used to pump out of the back of diesel cars in days gone by.

Whatever car you drive the method is similar: as the exhaust gases pass through the DPF any large soot particles are captured and stopped from causing problems. If the DPF becomes blocked there is a danger that your engine will stop running and you could be faced with an unpleasantly large repair bill that could easily run into thousands.

DPFs have limited capacities so need to be cleaned on a regular basis. This is done in general by the soot being burned at high enough temperatures for the debris to be broken down into small enough particles that can be expelled.

Common Causes of Failure?

Issues with DPFs arise when this process, known as ‘regeneration’, is disrupted. This can happen if the process doesn’t have long enough to be completed. Motor manufacturers advise that regeneration to clear the filter should be done by the car being driven car for over 15 minutes at more than 40mph and at intervals of around 300 miles.

If it’s not possible for the DPF to be regenerated passively in this way, a modern diesel car is fitted with an onboard computer that is set up to attempt “active” regeneration. Active regeneration involves the necessary action being taken by the car to stop the filter clogging up.

So, when the car’s computer detects a DPF is on its way to being blocked, it will increase the exhaust gas temperature to a level where regeneration is triggered. This process can last for between 10 and 15 minutes from start to finish.  

Disruption to the passive regeneration process can happen when the car is used for a lot of short, urban journeys, or the destinations are reached before regeneration has finished. On these occasions, the DPF warning light will likely come on. And when this happens you need to allow the DPF to regenerate by driving the car on a fast road like a dual carriageway or motorway for 15 minutes or more.

Ignoring the warning light and continuing to drive slowly in halting traffic carries great risks. It could switch the car to a limping mode in order to prevent any additional damage to the engine.

When replacing a DPF becomes the only option, be aware that if the problem has been caused by your driving style and not the filter itself, most manufacturers’ warranties will not cover the cost, which is liable to be expensive.

Why is a DPF required?

DPFs are required because they became compulsory under Euro 5 legislation which came into force 10 years ago. These regulations were brought in to restrict exhaust emissions, particularly CO2 emissions and it’s now illegal to drive any car that doesn’t meet its emissions standards. Since 2014 the DPF has been checked as part of the MOT test procedure.

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 an 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 Saffron Autos 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.

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