Diesel Particulate Filters

What is a DPF?

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A DPF (Diesel Particulate Filter) is a device fitted to many modern diesel vehicles within the exhaust system. The DPFs role is to filter out the soot particulates within the engine exhaust gases which is why the current BMW and MINI diesel range have spotlessly clean exhaust tips. Unfortunately, the reliability of the DPF systems is an issue for all vehicle manufacturers.At the time of purchase very few customers are informed of the product limitations regarding DPFs. To work correctly the filter harbours soot in a honeycomb structure and when the vehicle is very hot, normally at motorway speeds for 30 minutes, the car will automatically begin a ‘regeneration’ of the filter by switching on the glow plugs and injecting additional fuel to burn off the soot. If the type of driving you primarily do is short town journeys this will lead to the filter blocking up, bringing the warning light on and eventually hindering performance. In other cases a fault with the car such as glow plug malfunction will prevent this soot burn off procedure from occurring.

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In the event of a blocked DPF we will perform an exhaust back pressure test and carry out diagnostic checks to ensure there is no fault with the car which has caused the problem. Once we are satisfied the engine is operating correctly we will conduct a motorway road test for approximately 1 hour with the computer attached so we can force the car to enter the regeneration mode and burn off the soot. We will then carry out a second back pressure test to check it has been effective.

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In cases where the filter has been blocked for some time it may require removal to be soaked in chemicals before refitting and reattempting the regeneration. If this still proves to be ineffective we can replace the DPF so it functions normally again, however if it is deemed to have blocked up because the car is used for mostly short journeys the fault will still reoccur even though the car has been put back to perfect condition. In these cases it is possible to remove the core from the DPF and recalibrate the engine computer accordingly so it no longer requires a DPF, this way the fault won’t return although there will be typical sooty diesel deposits from the exhaust – however it must be stressed this is not compliant with current MOT regulations.

 

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