There are few things more unpleasant for motorists than being stuck behind another driver whose exhaust is spewing out black, sooty fumes. Not only does it mean you need your windows closed to avoid breathing it in, but it is bad for the environment as a whole.
However, there is always the danger that it could be you and your car in such a situation. This can depend on the state of your exhaust, not least the DPF filter.
A DPF filter, or a diesel particulate filter to give its full name, is something you will probably have fitted to your exhaust if you own a diesel car. It is not a new innovation and they have been around for approximately 20 years. They are in place to help filter out a lot of the particulate matter produced by burning diesel fuel, leading to cleaner air.
Indeed, they were effectively made mandatory by the introduction of the Euro 5 exhaust emissions standards into UK law in 2009, something that hasn’t changed since Brexit.
They work by trapping soot, but this builds up and therefore must be burned off to recreate more capacity. This helps ensure the filter is not suddenly churning out the excess soot – something that black smoke signifies.
As the RAC notes, it is illegal to remove the filter and this can lead to big fines (up to £1,000 for cars and £2,500 for vans), as well as invalidating your insurance policy.
Therefore, if you have got to the point where your exhaust is starting to belch out black smoke, you may need to call into our garage to have the DPF cleaned. Indeed, if is blocked you will definitely need this and an orange light will light up on your dashboard to tell you.
Sometimes, the blockage of soot becomes such that it will not burn off in the way it should. Rather in the manner of a blocked drain needing to be fixed by a plumber, a mechanic will be required to carry out a manual procedure. Â
Ideally, this will be a mechanic with specialist DPF skills, which means they can examine the filter, identify where the blockage is and clean it, after which you can get back on the road.
The technique involved is known as a ‘forced regeneration’. This is opposed to ‘active’ regeneration (where extra fuel is injected into the exhaust to increase the temperature and burn off the soot) or passive regeneration where the temperature rises high enough to burn it off anyway. This can happen on long drives at high speed, like a motorway journey.
In an ideal motoring world, a passive regeneration would happen almost by accident, so you wouldn’t have to think too much about your DPF at all, especially if long motorway journeys are the norm for you. Failing that, an active regeneration should do the trick.
Should neither do so, however, help is at hand, ensuring that your sooty problem can be resolved and you can drive on without leaving a hideous black trail behind you.