Diesel Particulate Filters are often considered within the industry to be consumable items. This means that their lifetime is considered variable and unpredictable and therefore in the category of Tyres and light bulbs!.
Whether a DPF (Diesel Particulate Filter) failure is covered under warranty depends on exactly what is stated in the Car owners’ manual. Many Car manufacturers advise that their diesel engine cars are not used for frequent short journeys as this does not allow the diesel particulate filter time to regenerate. Using a diesel car for city driving is also frowned upon because the car is unable to cruise at a steady speed in order for the engine and exhaust to reach the correct parameters in order for a regeneration to occur. Suffice to say, very few manufacturers will include the DPF system as part of the manufacturer warranty.
It would be easy for a car manufacturer to check the use of the vehicle largely just by checking the mileage that the car travels per year from new. So for example, if a car only does 2000 – 5000 miles per year, then it would be fair to assume that it is being used for short journeys or for the School run, neither of which would be commensurate with the advice in the manual in relation to doing regular motorway runs in order to protect the integrity of the diesel particulate filter, and giving the manufacturer a get out of jail free card. However, some manufactuerers don’t even go to this effort, and will just state that the DPF system is not included in the Car Warranty, and should it become blocked then it will be the owner who ends up footing the bill.
Diesel Particulate Filters are expensive, and it is fair to say that many car manufacturers would love to find a reason to avoid paying the four figure cost of replacing the DPF system at their expense, even when the car has its original warranty. You can of course, play the goodwill card, however any goodwill contribution from the manufacturer would be determined on a case by case basis, depending on the car use and its history.
Its largely considered that a car fitted with a Diesel Particulate Filter, should cover at least 12,000 miles per year, in order to keep the DPF system healthy, and therefore any goodwill warranty repair would probably depend on how far below that figure the car was being driven. It will also depend on the car being presented for servicing at the correct times, and also the correct oil being used.
It’s also wise to present your car for any warranty consideration as soon as the DPF warning light appears and a regeneration drive fails to reset it, the longer you leave it, the more blocked the DPF will become and the more expensive the problem will be to rectify and the less likely you will be to get the dealer to foot the bill. Taking a car under warranty to the dealer for a warranty repair as soon as a regeneration attempt fails, means that it could probably be solved by cleaning or a dealer forced regeneration, which, being much cheaper, is more likely to be carried out under warranty, than ignoring the Particulate Filter warning light, to the point where the filter itself becomes blocked beyond repair and requires replacing, at which time the dealer will be likely to blame the issue on your driving style, or not acting on the issue quickly when the warning light appeared.
If the dealer refuses to cover the cost of replacing the DPF whilst the car is under warranty please read our guide on claiming a DPF Repair / Replacement using the Sale of Goods Act