Diesel Particulate filter - Sterling Garage

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Diesel Particulate filter

About your car
The purpose of the Diesel Particulate Filter (DPF) is to prevent soot, from unburnt fuel entering the atmosphere. 
It is an important item on late diesel cars so much so that DVSA (the MoT authority) have issued a warning to Authorised examiners that they must check that if a DPF was fitted as standard, it must be in place at time of test. They have also said that any garage which offers MoT testing, removes or bypasses the filter, will bring the Mot scheme into disrepute and may have their testing licence removed. The DPF, they have also said, plays an essential environmental role in enabling reductions in emissions to help meet the strict European standars , reducing air pollution and improving health quality.
As can be seen from the small clipping from a professional magazine, it is not easy to recover a blocked system especially when the car's computer memory has logged the fault and wants to ensure that the unit is returned to pristine condition even when a new unit is fitted.
The driver does need to understand what this unit will do to the vehicle performance if the pressure sensors fitted in the system sense a blockage. Generally, the first indication that the DPF is starting to block will be when it is about 45% blocked. The build up of soot is generally caused by short local driving but may also be caused by a faulty EGR (Exhaust Gas Recirculating) valve. Initially though the blockage is usually due to the driving style and conditions which do not allow the engine to do its own active regeneration.
The question really is how does the driver burn off this soot blockage and what is happening with the DPF. To initiate the automatic burn off sequence, the vehicle has to be driven at a constant throttle for a set period of time, usually several minutes. When the engine determines that an active regeneration is required, the EGR system is closed off to provide increased oxygen to the exhaust along with secondary bursts of fuel into the cylinders just after combustion allowing the Oxygen mixture and unburned fuel into the ceramic core of the DPF which superheats to as much as 500deg C, burning off the soot deposits. This should be considered to be a regular maintenance item by the driver probably when oil levels etc are checked, but monthly at least.
If the DPF reaches a blockage figure of 75% the the warning light will come on and the car may go into the limp home mode. If the system gets to this level then a technician needs to carry out a forced regeneration using a scan tool. The addition of a DPF cleaner into the fuel tank will also assist this process. This option will normally resolve a problem rather than spending two or three hundred pounds on a replacement unit but will depend on the amount of soot held in the DPF. There is no way of determining this and whilst it is the correct and economic course of action may require a new DPF if the blockage has become too great. This repair may not work if the light has been on for too long and the filter has gone past the 75% level but it's always worth a go.
The important lesson with those vehicle fitted with a DPF is to ensure that the driver gets a run on the open road on constant throttle and as an option, if most of the work is local town work, put a can of DPF cleaner and Regenerator every third tank. It's worth the cost as replacement can be expensive and most garages feel that when renewing the DPF other associated components should also be renewed, the EGR valve oil and air filters. If you don't drive it, you will lose it.
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