If you are considering leasing a car or van with a diesel engine, it’s worth noting that most diesel vehicles are fitted with a Diesel Particulate Filter (DPF) and/or require Adblue Solution/exhaust fluid. This is so that the vehicle can meet strict emission rules. You will find more information about AdBlue/exhaust fluid here.
The purpose of this information is to highlight that a vehicle fitted with a DPF is not always suited to short journeys or start/stop town driving. If you mainly do low mileagetown driving, you may want to consider electric or petrol vehicles instead
YOUR VEHICLE USAGE AND ITS DIESEL PARTICULATE FILTER (DPF)
Most modern diesel cars are fitted with a Diesel Particulate Filter (DPF) to meet European emissions standards, but they can cause problems for drivers that use the vehicle for start/stop town driving.
WHAT IS A DIESEL PARTICULATE FILTER (DPF)?
The DPF is a filter that captures and stores exhaust soot (some refer to them as soot traps) in order to reduce emissions from diesel cars. But because they only have a finite capacity, this trapped soot periodically has to be emptied or 'burned off' to regenerate the DPF.
This regeneration process cleanly burns off the excess soot deposited in the filter, reducing the harmful exhaust emission and helps to prevent the tell-tale black smoke you used to see from diesel vehicles, particularly when accelerating.
A DPF can remain effective for a long service life through repeated cycles of trapping particulate matter and regeneration.
HOW DOES ‘REGENERATION’ OCCUR AND WHEN CAN IT CAUSE AN ISSUE?
There are two types of regeneration: passive and active.
Passive regeneration occurs when the car is running at speed on long motorway journeys which allow the exhaust temperature to increase to a higher level and cleanly burn off the excess soot in the filter.
So it is advised that drivers regularly give their diesel vehicle a good 30 to 50 minute run at sustained speed on a motorway or A-road to help clear the filter.
However, not all drivers do this type of driving regularly – which is why manufacturers have designed an alternative form of regeneration.
Active regeneration means extra fuel is injected automatically, as part of the vehicle's engine control unit (ECU), when a filter reaches a predetermined limit (normally about 45%) to raise the temperature of the exhaust and burn off the stored soot.
Problems can occur, however, if the journey is too short, as the regeneration process may not complete fully.
If this is the case the warning light will illuminate to show the filter is blocked - check your handbook for more information.
It should be possible to complete a regeneration cycle and clear the warning light by driving for 10 - 30 minutes or so at speeds greater than 40mph. It is important that this is done at the earliest opportunity.
The best place to do this is a motorway or on a long stretch of dual carriageway.
You should always drive the vehicle in a safe manner according to traffic conditions and obey current, local traffic laws.
What do I do if neither active nor passive regeneration work?
If, after the DPF warning light illuminates, regeneration does not work or the vehicle continues to be driven in a style whereby the exhaust gas temperature cannot be raised sufficiently, then the vehicle’s electronic control system kicks in to protect the DPF and the engine.
The engine warning is illuminated together with the DPF warning lamp - check your handbook for more information - and the vehicle may also enter “limp” mode and limit engine speed to a maximum of 3,000rpm.
Once the engine warning lamp is illuminated, driving at higher speeds will not regenerate the DPF and it is imperative to get the vehicle checked out straight away.
Otherwise, more damage can be caused and what could be an inexpensive fix can quickly become very expensive.
Some garages can clean blocked DPFs, in a process called forced regeneration. While it’s not a 100% guaranteed fix, it’s usually successful in removing the excess soot and allowing the DPF to work and automatically regenerate again.
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