What on earth is a DPF filter we hear you ask? Many motorists may never have heard of a DPF. For those that have, there’s a good chance the discovery was made after a warning message appeared on the vehicle’s dashboard, but what does the warning mean and why is it important?

So first off, what is a DPF and do all vehicles have one?

DPF stands for ‘Diesel Particulate Filter’, commonly referred to as a DPF Filter despite the iteration of the word ‘filter’! 

The biggest hint regarding which vehicles possess a DPF is in the name itself. DPF Filters are indeed, exclusive to diesel engine vehicles but they can be found in all types of diesel vehicles including road cars, heavy-goods vehicles, motorbikes, agricultural vehicles such as tractors and even motor boats!

But what does a DPF filter do and why do we have them?

DPF filters were first made mandatory on all newly manufactured diesel vehicles back in September 2009 as part of the Euro 5 standards. Whilst some vehicles produced before this date featured a DPF filter, it was only after this date that ALL diesel vehicles HAD to include one in order to comply with standards. 

The sole purpose of the DPF is to filter, store and then burn, harmful soot from the diesel engine’s emissions. 

Whilst the process itself is vastly different, a DPF filter could be compared to a catalytic convertor found on petrol vehicles in that its main job is to reduce the dirty emissions that are emitted from a combustion engine. 

What happens to the soot?

The soot that is collected inside the DPF filter is burnt off. This process is called ‘regeneration’. Regeneration occurs in one of two ways; passive or active. 

Passive regeneration occurs whilst the vehicle is being driven, using the heat from the exhaust to burn off the soot and turn it into ash. For this to work, the vehicle ideally needs to be driven for at least half an hour or so at motorway speeds. 

Because this is not always possible due to shorter journey requirements, speed limits and slow-moving traffic, manufacturers added an ‘Active Regeneration’ process to DPF filters. ‘Active Regeneration’ works by injecting a small amount of fuel into the DPF to help quickly increase the temperature of the filter and burn the soot off effectively. With that said, Active Regeneration still requires speeds upwards of 40mph for at least 10 minutes.

Why does a DPF get clogged/blocked up?

As you can tell, active and passive regeneration only really works under certain conditions, neither of which are always possible, particularly in urban areas across the UK. For anyone making the morning commute or picking the kids up from school, you’ll know anything over 20mph can be a luxury despite how long the car is running. 

If the regeneration process can’t kick in often enough, the soot that your DPF filter has been collecting will continue to build up until such a time that the filter becomes blocked altogether. 

What happens when the DPF becomes clogged/blocked?

Your vehicle will more than likely tell you about it via a dashboard warning light or message. The message can vary depending on the vehicle manufacturer but it’s one you shouldn’t ignore. Whilst some vehicles will give you ample warning that your filter is blocked, other vehicles can immediately drop into ‘limp mode’. ‘Limp mode’ will force your vehicle into a low-power mode that will barely give you enough ‘oomph’ to get to your nearest garage. 

Other effects of a blocked DPF filter are poor fuel consumption, reduced performance or worse, permanent damage to the filter and potentially even the engine or turbo leading to extremely costly replacements!

What should I do if I see the DPF warning light?

If your DPF warning light comes on, providing it’s safe to do so, stop the car and turn the engine off. Don’t attempt to make unnecessary journeys. If you can, find a local garage that will help to confirm the diagnosis.

A DPF warning light does not necessarily mean your DPF filter is done for. Replacement DPF filters can be eye-wateringly expensive, often costing several thousand pounds, exclusive of labour costs. Always seek out a second opinion if you feel your mechanic may be unnecessarily charging you for a replacement filter. 

9 times out of 10 DPF filters can be cleaned to near-perfect health.

How do I clean a DPF filter?

Whilst relatively straight forward, cleaning a DPF filter isn’t a DIY job and required special equipment and training. Attempts to clean or replace a DPF filter yourself will likely cause more damage than good. 

That said, it’s not a particularly expensive or time-consuming process for a professional to carry out for you. DPF Cleaning can be carried out by mobile technicians, often ‘whilst-you-wait’. The process, which involves a special machine, can be completed roadside, at home or even at your office.

The cleaning process will remove any remaining soot or ash from inside the filter and restore your DPF to almost new, removing dashboard warnings in the process. For vehicles stuck in limp-mode, your vehicle will acknowledge the cleaned filter and restore your vehicle to full power. 

How often does a DPF last and how often does it need cleaning?

A DPF filter, providing the right driving conditions are met for effective regeneration, should last for at least 100,000 miles. This could be extended providing the DPF is well maintained which is why regular DPF cleaning is highly recommended. An annual DPF clean could drastically extend the life of your filter, preventing the need for a costly replacement further down the line. 

Can I remove the DPF Filter altogether?

That’s a solid ‘No’.

Whilst it’s not physically impossible, it is illegal to drive a vehicle that has had the DPF removed and not replaced. Removing a DPF will not only result in a failed MOT, but it can also invalidate your insurance and potentially land you with a hefty fine of up to £2,500.