What is a DPF (Diesel Particulate Filter)?

ByIsaac BoberAugust 20, 2019
What is a DPF (Diesel Particulate Filter)?

Every new diesel vehicle built (ex-Europe) since 2009 has a diesel particulate filter (DPF) but what is it and how does it work?

We all know how harmful diesel emissions are and the introduction of Euro 5 emissions regulations in Europe in 2009 sought to curb the Big Three: carbon dioxide (CO2); Nitrogen Oxides (NOx); and particulates (see, reducing NOx causes an increase in particulates. The intention of Euro 5 was to reduce emissions and cut the pumping out of cancer-causing particulates, as a result, by 80 percent. Euro 5 regulations made it mandatory for all new Europe-built diesel vehicles to be fitted with a diesel particulate filter.

Exhaust Gas Recirculation…does that work?

Plenty of car makers have experimented with exhaust gas recirculation on diesel engines to help reduce NOx emissions. And, it works. It does this by directing ‘an amount’ of exhaust gas into the engine’s air intake and reduces the amount of fresh air needed. But this ends up reducing cylinder temperatures and thus increases particulate matter…and that’s bad because diesel particulates cause cancer.

What does a Diesel Particulate Filter do?

As it says on the box, a DPF is there to catch diesel particulates (or soot). Indeed, it’s designed to reduce the amount of particulates making it out into the atmosphere by 80 percent. However, because a DPF, just like any filter, has a limited capacity to filter before it becomes clogged, it has a bunch of sensors built in that will see it burn off the particulates once it fills to around 45 percent, and this is called ‘regeneration’.

How Does A Diesel Particulate Filter Regenerate?

There are two ways in which your vehicle will ‘regenerate’ the DPF and these are either via ‘passive’ or ‘active’ regeneration.

Passive regeneration occurs without the driver knowing when the vehicle is running at, say, highway speeds for a sustained period which is usually around 30 minutes or longer. This allows the exhaust temperature to heat up to burn off the particulate/soot (usually around 600 degrees).

Active regeneration was introduced to ensure those drivers who only drive short distance and thus don’t meet the threshold for passive regeneration could still have the particulate in their DPF burnt off. Once the filter has filled to a certain capacity and the vehicle is being driven, extra fuel will be injected to help increase the exhaust temperature and burn off the particulate. When active regeneration is in process it’ll usually take around 15min of driving at around 60km/h or more in top gear.

How Do I Know If My Diesel Particulate Filter Is Blocked?

If your car’s DPF hasn’t regenerated and has become ‘blocked’ you’ll see a warning light on the dashboard like the image below.

DPF Full symbol

Why Would My Diesel Particulate Filter Become Blocked?

Simple, you’re driving only short distances and at low speeds which is either too short and too low a speed for either passive or active regeneration.

How long does a DPF last?

Most car makers suggest a diesel particulate filter will last around 160,000km before needing replacement.

Can a DPF fail?

Yes. Just ask Toyota. Generally speaking, though, your DPF shouldn’t cause too many problems as long as it regularly regenerates. Most car makers suggest a DPF will last for around 160,000km before needing a replacement.

Does a DPF regeneration increase the risk of a grass fire with your 4×4?

Anything that causes an increase in heat underneath your vehicle while you’re driving across long grass is an increased fire risk. Depending on the speed you’re driving at, it’s unlikely the DPF would regenerate while you’re in long grass but it’s still something to be mindful of.

What If a DPF Warning Light Stays On?

If you’ve taken your vehicle for a good highway run and the warning light is still on with a check engine light also illuminated, then you’ll need to take your vehicle to a mechanic. If you’ve turned your car off and then on again and the DPF and engine warning light are both still on, then you shouldn’t drive the vehicle. You don’t want to let a DPF issue go unchecked because your vehicle is likely to go into limp mode and, if the worst happened, and the DPF ends up needing replacement, then you could be up for thousands of dollars in replacement costs. Getting a blocked DPF unblocked by a mechanic might only cost a few hundred bucks.

Should I delete my DPF?

No. Some diesel mechanics offer a DPF delete (or bypass) for when you’re driving off-road but it’s illegal to have the DPF in your vehicle deleted. Indeed, the fine for individuals is more than $20,000 and for a company caught deleting a DPF the fine can be up to $1million.