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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.

16 Comments

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  • This article doesn’t mention the main reasons for excessive DPF regeneration and early failure. Split turbo/intercooler pipes, high oil levels, sensors blocked with carbon/oil gunk and carbon/oil gunk build up inside intakes. All of this can cause the engine to soot up the DPF faster, makes it burn off more frequently and leads to early failure, (ash blockage). DPF failure is a symptom of another issue, that issue is a poorly maintained engine. DPF’s can be opened up and cleaned out for a fraction of the manufacturers replacement price. ($600 vs $3500+ !!) Modern diesels are fantastic engine’s and perform better than both old diesels and old/new petrol engine’s. But if you don’t understand how they work, you will get ripped off by a dealer or a mechanic. Stick with what you know and leave the diesels for the people who know them.

  • With all this potential concern I’ll stick with my 2005 100series factory Turbo Diesel Cruiser. With close to 450,000Ks on the clock (always well serviced), it still runs fine. The fuel consumption is consistent even when towing my 3T van, no oil use between changes every 5,000Ks and still with the original injectors. It may not be the fastest rig up the hills but it’s low down grunt when it counts is great. It’s most happy to cruise at 90 when towing, the truckies get around me without worries when we speak on the UHF and I also get to safely look at the scenery. All this at true all round diesel running benefits.

  • Great article. And that’s another reason why I stay with my old diesel 4×4. New diesel cars & 4×4’s ? No way. There’s to many new this new that & now makes them a probable breakdown and expensive to calculate & run. Not to mention costly rebuilds of common rail fuel systems when minute particles stuff up pumps & injectors from not so good fuel. Rebuild the Pre DPF & common rail 4×4 models & be happy I say. Function & reliability is important. New Diesel 4×4 are getting way too expensive wait till the problems evolve in the 2nd hand market. My view.

  • It’s hard to justify buying a diesel these days. Economy is no better than a petrol. Exhaust temps are just as high, when traditionally they ran much cooler, there’s no where near the engine braking capacity. And reliability, and running costs are on par, or worse than petrol engines. Toyota probably retired the 4l V6 5 years to early. They’d be flying out the door now.
    I do enjoy the V6 in the VW though.

  • I’m having the DPF replaced in our 2015 Subaru Outback it’s done 200000k’s and the cost to replace it is $4700. My issue apart from the cost is when you purchase the vehicle no one advises you that anywhere between 150000 and 200000 kilometres you will need to spend around $5000 for a DPF. Next vehicle won’t be a diesel

  • I wonder how many diesel buyers were aware of the problems with and more importantly the replacement costs for their DPF when they lined up to buy their new CRD rig? The trick is obviously to trade in and leave the $4-7K problem for the next buyer. Diesels have advantages but when you factor in the costs associated with fitting additional fuel filters and replacing expensive injectors the equation isn’t quite as rosy as many think.

    • Even if they do work ok, it’s something to eventually cost more money when it needs replacing.
      Diesel is starting to get complicated. Surely it’s better to just go back to petrol

  • I have heard some horror stories with DPF’s. It is one thing to say they last 160,000km’s. What they don’t tell you is that from my research the cost of replacement with many vehicles is between $5,000 and $12,000. This is just crazy. I feel like this has not had the attention it deserves. A part worth this much should not be considered a consumable and people need to made aware of this when purchasing diesel vehicles. 🙁

  • I’ve got a DPF on a Toyota Land Cruiser. Faultless operation for 3 years so far. Don’t even know it’s there.

    Generally this is true of the DPF on that model. Forums report few problems.

    So they can be made to operate seamlessly. Toyota know how to do it. They need to step and properly address the issues seen on other models.

  • My Navara (2009) split open the DPF filling the cab with fumes on arriving at Alice Springs after driving from Newcastle NSW a $5,500 fix at 130000 k’s. How many others out there have had a similar experience, never buy another Diesel.

    • I also have a 2009 Navara and have had to replace the DPF because it was blocked and had started to colllapse internally, nearly $4,000 with an after market DPF, Nissan DPF would have cost heaps more.
      The replacement should be covered by the manufacturer, maybe they would then manufacture a DPF that doesn’t require replacement.

  • I’ve contacted my Toyota dealer and the lady there said there is no problem “it’s all just media hype”. I contacted Toyota. She told me to take my car to Toyota dealer if the car has issues. What happens when, not if the car fails when the warranty has expired. Not happy Jan!

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