Diesel Particulate Filter - what's that?
The MOT has changed recently to include the diesel particulate filter (DPF). This is due to the EUV directive covering emissions and was brought in during 2009. Manufacturers may have added the DPF before this. It's worth checking with your car's manufacturer to see if it needs doing.
When you take your car into the local garage for your MOT, the mechanic will now have to look at your filter. Firstly, to make sure it's still there and hasn't been removed. It's illegal to remove the filter and also reduces CO2 emissions from entering the atmosphere. If the DPF has been removed from your car, you will automatically get an MOT failure notice and be prosecuted. Secondly, a smoke emissions test is carried out.
Diesel cars need to be driven to burn up the soot that accumulates in the ceramic filter. The DPF is located within the exhaust system and captures soot, stopping the particles from being sent out into the atmosphere. It's been described to me, by the mechanics in our garage next door, like a fireplace. Soot gets burnt away, but you're left with a small amount of ash, which has to be disposed of. This is called regeneration.
If you do lots of motorway driving or long journeys, this should happen automatically. However, if the warning light comes on, drive your car for at least 10 minutes at 40mph or more to see if this will start the regeneration process. If the warning light doesn't clear, the filter could be blocked and it may need to be cleaned out by a mechanic. Apparently Mercedes can only be driven to start the regeneration process.
Warning lights on dashboard for DPF failure.
Next time you want to change your car, think about your lifestyle, do you do lots of short journeys and would a petrol car be more economical if you're an urban driver.
If you would like further information on any of the above or advice on used cars, please do not hesitate to contact us.
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