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The Dreaded DPF and Removal



We know what most of you are thinking, the dreaded Diesel Particulate Filter. All modern day diesels will be fitted with a Diesel Particulate Filter (DPF) Its primary function in its simplest terms is to reduce the pollution output from your vehicle and make the exhaust gases cleaner and more environmentally friendly. 

So how does it work? The dpf filter has a fine element that is designed to catch the particulate matter present in the exhaust gases produced from a diesel. This matter is then trapped in the filter element. A pressure sensor then monitors the differential pressure in the exhaust. The more matter that is trapped, the higher the pressure becomes. The engine management system monitors this build up and when the time is right it will clean the filter through a regeneration process. Depending on the type of system your vehicle is fitted with will depend on how this regeneration is achieved. It is required that the vehicle is driven (ideally down the motorway) at a constant speed to allow the temperature of the filter to become hot enough to burn off the particles cleanly inside. If you do not get chance to run your vehicle in this way then sometimes the regeneration process cannot be completed. This can cause the filter to become over loaded and a forced regeneration may be necessary. This can only be done with the correct computer software and should not be done to frequently or it can damage the DPF.

Some vehicles mainly Citroen and Peugeot use a diesel additive that is injected into the diesel from a separate tank each time you fill up with fuel. This allows the particulate matter to burn off at a lesser temperature. It is important that the level of this additive is checked and topped up as running out can cause the DPF to block up. 

So What Happens When Something Goes Wrong?

Invariably as with all things the system is going to fail and the panic is likely to set in. It is not always the DPF that is at fault when the system fails. There are various temp sensors, pressure sensors, and other components that can effect the regeneration process but if you are unlucky enough to have a failed DPF then the repair can get quite costly. 

Should I remove My DPF?

The first question we usually get asked is can you remove the DPF and do away with it. The simple answer is it can be done but it is not recommended. Removal of the DPF is illegal and will be checked at MOT time to see if the filter is present. Many people get around this by just removing the insides of the filter and keeping the shell so that it can been seen at the time of MOT and therefore will not cause it to fail. 

It doesn't just stop there. You cannot successfully remove the DPF without making alterations to the engine management computer. This is where most of the problems kick in. There are a lot of places that will offer you DPF delete, but it is not always that simple. Most will use a generic software to try to delete the DPF function. The generic software will attempt to delete the coding strings that relate to the DPF, but this software will not be able to delete all the files. The file structure for the DPF is linked into other systems like fuel rail pressure, exhaust gas temperature etc.The coding strings for these sensors cannot be deleted or it would cause data corruption, but just left there are now random file parts that are left in the ECU and can cause it to keep going into limp mode. 

It gives much to think about before removing your DPF. It's not nice having to pay for repairs on your DPF but sometimes it can cost you more trying to remove it. Its arguable as to whether it is cheaper to run a petrol than a diesel. Ok so your diesel may get more miles to the gallon, but there is no getting away from the fact that eventually you are going to have to spend out on repairs to the DPF, high priced diesel injectors or maybe even injection pump. So over all you are financially no better off than running a petrol that might get less MPG but doesn't have all those expensive parts that a diesel does.

As auto electricians and French vehicle specialists we see these faults all the time. We have had many calls from people that have had DPF's removed, and the management light has come on with running problems. In my opinion DPF removal may not always be the right way to go but I'm sure there are plenty out there that will disagree.   




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