Diesel Particulate Filters
Diesel particulate filters (otherwise known as DPFs) are a filter installed on the exhaust system of modern diesel vehicles in order to greatly reduce the level of soot emitted out of the vehicle into the atmosphere. The soot particles are trapped in the DPF until a sufficient exhaust temperature is reached to burn them off turning the harmful particles into carbon dioxide, this is called DPF regeneration.
One of the main issues discovered on vehicles equipped with a DPF is that the filter can get blocked if the vehicle is only frequently driven on short urban journeys because the exhaust system will not reach the temperature required for DPF regeneration.
This is an issue that a lot of modern Jaguar and Land Rover owners will know all too well, as many buyers have opted for diesel due to its better fuel efficiency vs similarly sized petrol models.
Symptoms Of A Failing DPF
Blocked DPFs usually present a few symptoms, including triggering an engine management light and sending the vehicle into limp mode. Some vehicles will also show a red DPF light on the dash and display a message saying “Exhaust filter full visit dealer to clear” or similar. At this point diagnostic equipment is needed to try and force a regeneration to clear out the system, if that doesn’t work, cleaning of the filter can be attempted, and if that still does not allow for the fault to be cleared, a new DPF will be required and due to the exotic materials used in their construction, these are not cheap.
Because of their cost, it is better to keep the DPF clear and passively regenerating by itself regularly, you may even see a yellow warning light informing you that a regeneration needs to take place. This is achieved by regularly running the vehicle at motorway speeds for 30 minutes or more, if this does not happen, and the temperatures associated with motorway speeds are not regularly reached, the DPF will attempt an “active regeneration” where extra fuel is injected during combustion to force raised engine temps, the issue with active regen is that this extra fuel won’t all be burnt off on a short journey and the unburnt fuel will dilute the engine oil over time, weakening its lubrication properties. This means that unless the oil is changed regularly, there is a chance that the engine will not be lubricated properly, generally leading to a turbo failure or potentially an engine failure. At K Motors we have actually seen engines with fuel making up 40% of the oil contents in the sump!
This table below contains a list of Land Rover and Jaguar models using diesel particulate filters
How To Tell If Your Vehicle Has A DPF?
As mentioned in the table above, most modern diesel JLR vehicles are equipped with a DPF, but if you have a model in those first few years where particulate filters transitioned from being an optional extra into standard equipment, there can be some confusion. Some will say if your tailpipes are angled downwards, you have a DPF, others say the opposite. Realistically, the easiest way to tell is to have a look underneath the vehicle and see if you have a bulky cylindrical chamber downstream of the manifold but in front of the first silencer.
It is also worth noting that new petrol vehicles are being equipped with similar filtration technology now as well in order to adhere to ever tightening emissions regulations but this will not be common practice for a few more years.
What Should I Do If My Car Has A DPF?
If you have a vehicle equipped with a DPF and regularly drive at high speeds for 30 minutes or more, there is no need to worry. If you use your vehicle for short journeys however, you will need to be mindful of when an active regeneration is in progress (characterised by a raised and lumpy idle and reduced fuel consumption as well as a warning light on some models) and ensure the regeneration cycle is completed before switching off.
It is also strongly recommended that you get your oil changed at least once a year to ensure the engine is not running on diluted oil, even if your car is not telling you that you need a service yet.