All modern diesel cars come with a Diesel Particulate Filter, or DPF.
DPF stands for diesel particulate filter and its job is to filter out the toxic and microscopic particulates emitted in your car’s exhaust. The trouble is, because of the way it works, a DPF can cause expensive problems if not treated properly.
What is a DPF filter?
Diesel engines burn fuel differently from petrol and produce a lot of soot in the process. This soot is known as particulate matter. It’s a very fine, almost invisible substance that can cause serious health problems if allowed to enter the environment. The job of the DPF is to filter and trap it before it does. Its fitment was made mandatory in 2009 so all diesel cars built and sold since then, have one. Even some diesel cars made before 2009 have a DPF.
The DPF not only traps and hold particulates but it can also burn them, turning them into a harmless ash that is emitted through your car’s exhaust system. It does this by burning them at a high temperature in a process called DPF regeneration.
DPF regeneration and why diesels are bad for short journeys.
There are two types of DPF regeneration but both require the exhaust gases to reach a very high temperature, typically around 500 degrees Celsius.
Such a temperature is achieved when driving above 60mph for around 12 minutes. Doing this on a regular basis is enough to burn off the soot and turn it to ash. Unfortunately, drivers who live in the city or who do not travel very far won't get their car up to a high enough operating temperature to achieve this. Levels of soot can build up, causing the DPF to become blocked which in turn leads to engine problems including reduced economy and misfiring. If you don’t drive at speed often, the engine will try to clear the DPF via ‘active regeneration’. This is where the engine lets the exhaust gases get hot enough to burn off the soot without requiring the car to be run at speed. Unfortunately, active regeneration can only take place when the car is moving, so town drivers – who typically drive in stop-start traffic like cab drivers – may find their cars are unable to actively regenerate the DPF.
If you see a warning stating "Risk of Diesel Filter Clogging" it referes to the DPF, you should be able to get the DPF to regenerate itself by driving over 60mph for about 20 minutes. If that does not remove the warning however, this means a trip to the garage is needed.
If you see a warning stating "Diesel Additive Level Low" it is vital that you get this filled up ASAP, this is the fluid that allows the vehicle to increase the exhaust to the high temperatures needed to regenerate. If this fluid is allowed to completely run out the vehicle cannot regenerate and the DPF starts to clogg up. Also when the additive tank runs dry the built-in pump can sieze requiring the tank to be replaced which trebles the cost of the repair.
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