How to Solve a Blocked Diesel Particulate Filter

Diesel drivers have often been told to make sure they take their cars out for a good long run every now and again to protect their DPF. But what exactly is a DPF? And why does it get blocked? Well, luckily Scrap Car Comparison has the answers, so read on to find out exactly what that weird warning light is telling you.

But first, if you’ve tried everything and can’t seem to get back on top of your DPF, then it might be time to jack it in completely. With Scrap Car Comparison, we can guarantee you the very best price for your car, no matter how bad its condition might be. With buyers in all four corners of the country, you’re never too far from being able to use our service, so get started today to see just how much you could save.

Close up of a DPF

What is a diesel particulate filter (DPF)?

A diesel particulate filter is designed to capture all of the soot to reduce emissions from diesel vehicles. However, these filters not only capture the soot, but also store it, so are prone to becoming blocked over time. As a result, these filters have a system in place to help burn off the soot – known as ‘regeneration’. This helps reduce the harmful emissions and also try to cut down on those big black plumes of smoke you see out the exhaust pipes of diesels under acceleration.

Symptoms of a blocked diesel particulate filter

Normally you’ll receive a warning on your dashboard to let you know your DPF has been blocked, which usually looks like a box with dots inside and a pipe running through the centre of it. This can vary from manufacturer to manufacturer, so if you’re not sure you should check your owners’ manual.

The onscreen warning message of a car with a blocked DPF

You may also find that your engine is stuck in ‘limp mode’ or cannot rev to the higher end of the dial. Other symptoms include a reduction in your fuel consumption, the smell of diesel in your cabin and those tell-tale plumes of black smoke in the rear-view mirror.

Why is my DPF blocked?

One of the most common reasons for a DPF blockage is the way you drive your car. If you only take short journeys, then your car won’t have reached the optimum temperature to begin the regeneration process and burn off the soot. This can also be influenced by traffic jams and the cold winter temperatures.

Using the wrong engine oil can also wreak havoc on your DPF, as can a failure in your turbo systems and simply not keeping up with a regular maintenance schedule. Finally, the sensors relating to your DPF could have failed, which are also regular problems for diesel drivers.

Can you remove your particulate filter yourself?

No. Removing a DPF is a crime and you could be fined up to £1,000 for owning a car or £2,500 for owning a van without a DPF fitted. It could also invalidate your insurance policy. 

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How to fix a blocked particulate filter

The simplest way to sort out a blocked DPF is to engage in ‘passive regeneration’. Simply put, this is driving on a motorway or A-road at a sustained speed for 30-50 minutes to allow your exhaust temperature to reach the point where it can cleanly burn off the excess soot.

Of course, this option is not always possible, so there is also ‘active regeneration’, where additional fuel is injected automatically, via the vehicle’s ECU, when the filter reaches a defined limit to try and increase the temperature to burn off the soot. You can tell if active regeneration is taking place by the following:

  • Change of engine note
  • Cooling fans active
  • Increase in fuel consumption
  • Increase in idling speed
  • Stop/Start technology deactivated
  • Acrid smell from the exhaust

If neither active or passive regeneration have solved your problem, the you’ll want to take your car to the garage sooner rather than later, as waiting too long could turn a rather small issue into something much more serious. Some garages will offer a service called ‘forced regeneration’, which will usually clear up enough soot to allow the other regeneration methods to kick in.

If it’s looking increasingly like you’ll need to completely replace your DPF, then prepare yourself for a hefty repair bill. Particulate filters are not the cheapest of parts, and can cost between £1,000 and £3,500 alone, meaning the older a car is, the less viable it becomes to replace one.

Would a blocked particulate filter make me fail an MOT?

The only official ruling surrounding a DPF on the MOT is that if the car was originally fitted with one, then it must be there in order to pass the test. If the filter has been removed, it’s an instant failure. While there’s nothing to say a blocked DPF will fail the test, if any of the symptoms flare up – particularly the thick black smoke out of the rear – then chances are you’ll also fail on this, and it could also cause you to fail the emissions element of the MOT, too.

How to maintain my particulate filter in the future

Knowing that a brand new DPF is likely to set you back a couple of grand, it’s worth doing all you can to stop it from reaching that point. The simplest way is to make sure you’re driving in a way that encourages the regeneration process. If you know that you’re only going to be carrying out short drives – less than half an hour and not at a constant speed – then it might be worth replacing your car for a petrol or alternative fuel equivalent.

Get the best price with Scrap Car Comparison

If your DPF is beyond the point of no return, but you simply cannot justify the cost involved in replacing it, then perhaps it’s time to say goodbye to the car as a whole. By using Scrap Car Comparison, you can guarantee the very best price for your car no matter its condition when selling to one of our scrap or salvage specialists. We only work with certified buyers, meaning your vehicle will be recycled in line with all legal requirements, and our collection service covers 99% of the country, so you’re never too far away to use Scrap Car Comparison. Get started today to see just how much your old car could be worth.

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