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Customer Factsheet
AdBlue® and the Diesel Particulate Filter (DPF), explained — what they do, the warning signs to act on, and who's responsible for what.
As part of the drive to reduce harmful emissions from diesel vehicles, technologies such as Selective Catalytic Reduction (SCR) and Diesel Particulate Filters (DPF) have become commonplace. Here's a brief summary of the key facts, so you've got what you need to make informed decisions and keep your vehicle running smoothly.
Selective Catalytic Reduction (SCR)
Used correctly, SCR is reported to help reduce Nitrogen Oxide (NOx) emissions by up to 90%, and could potentially reduce the fuel used by between 3% and 5%.
Vehicles with SCR are fitted with an additional tank designed to store a liquid reductant known as AdBlue®, which you can buy from selected vehicle dealers and fuel stations. Your vehicle manual will tell you which warning lights and sounds indicate it's time to refill the tank, and how to go about it.
Pay swift attention to AdBlue® warning signs. Ignoring them could see your vehicle go into ‘limp home’ mode (reduced power), or it may fail to restart once the ignition is switched off.
Just like fuel, the cost of refilling the tank with AdBlue® is the responsibility of the individual driver or their employer. However, where the service schedule states the fluid should be changed (rather than topped up), and this is covered by your maintenance agreement, that cost will be included.
Diesel Particulate Filter (DPF)
Almost all diesel vehicles are now fitted with a DPF, designed to catch soot in the exhaust and prevent it entering the environment.
To keep everything running smoothly, the filter needs to be regularly cleared through a process known as regeneration — soot is burnt off at high temperature, leaving just a small residue of ash. This happens automatically when driving at motorway speeds, because the exhaust reaches a high enough temperature for regeneration to occur.
Shorter journeys and forced regeneration
If a vehicle is mainly driven for shorter distances at slower speeds, this cleaning process won't happen often enough to keep the filter clear. In these circumstances, most vehicles will trigger a forced regeneration by boosting the exhaust temperature. This can mean driving for around 10 minutes at speeds greater than 40mph until the process completes and the warning light clears.
If the warning light is ignored, soot levels will keep rising and the vehicle may enter a ‘restricted performance mode’ to limit further damage. At that point, the vehicle will need professional attention to clean or replace the DPF — this can cost upwards of £1,000, and is not covered by warranty or any maintenance agreement.
To protect your DPF and keep it running smoothly, follow the guidance in your vehicle handbook and act promptly on any warning lights.
Sources
- Maryland Department of the Environment, Selective Catalytic Reduction (SCR) fact sheet — NOx reduction of approximately 90% and fuel economy improvement of up to 5%; corroborated by the Engine Technology Forum.
- Cotswold Petroleum, Top 5 Reasons Why AdBlue is Essential for Diesel Vehicles — effects of running out of AdBlue®, including reduced power and potential engine shutdown.
- RAC Drive, Diesel particulate filters: guide to DPFs, and The AA, Diesel particulate filters — filter cleaning and problems — both independently confirm the 10-minutes-at-40mph+ guidance for clearing a DPF warning light.
- The AA, Diesel particulate filters — filter cleaning and problems — restricted performance mode if ignored, and replacement cost of at least £1,000 plus labour.