Changes to new car emissions legislation scheduled for 2009, the so-called 'Euro 5' standards, will make particulate filters as
commonplace in diesel car exhausts as catalytic converters are on petrol cars. The goal is an 80% reduction in diesel particulate (soot) emissions.
When the particulate filter warning light illuminatetes it is indicating a partial blockage. Diesel Particulate filters (DPF) or 'traps' catch bits of soot in the exhaust.
As with any filter (think of the bag in your vacuum cleaner) they have to be emptied regularly to maintain performance. For a DPF this process is called 'regeneration'
.......the accumulated soot is burnt off at high temperature to leave only a tiny ash residue. Regeneration may be either passive or active.
Passive regeneration takes place automatically on motorway-type runs when the exhaust temperature is high. Many cars don't get this sort of use though so manufacturers have to design-in 'active' regeneration where the engine management computer (ECU) takes control of the process.
When the soot loading in the filter reaches a set limit (about 45%) the ECU can make small adjustments to the fuel injection timing to increase the exhaust temperature and initiate regeneration. If the journey's a bit stop/start the regeneration may not complete and the warning light will illuminate to show that the DPF is partially blocked.
It is possible to start a complete regeneration and clear the warning light simply by driving for 10 minutes or so at speeds greater than 40mph, engine RPM at about 2500, and a light throttle position.
If you ignore the light and keep driving in a relatively slow, stop/start pattern soot loading will continue to build up until around 75% when you can expect to see other dashboard warning lights illuminate too. At this point driving at speed alone will not be sufficient and the car will have to go to a dealer for regeneration.
If warnings are still ignored and soot loading continues to increase then the most likely outcome will be a new DPF costing around £1000.
If you buy a car with a DPF fitted it's important to read the relevant section of the vehicle handbook so that you understand exactly what actions to take if the warning light illuminates and how, if at all, your driving style may need to be adjusted to ensure maximum DPF efficiency and life.
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The DPF is designed to 'Burn off' the soot deposits that accumulate, but in order for this to happen the exhaust has to become really hot. The DPF will fill up if the vehicle does a lot of short trips and the exhaust fails to get hot. The cure is a long hard drive
Whenever this warning or any other stays on in the dash it is indicating that the systems control module has detected a fault, it then disables the system as long as the light is on. You must now have the dealer hook up a special electronic diagnostic tool and "scan" the system for the fault code that is stored for the problem(s)
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