Diesel Particulate Filter (DPF) – the essential guide

We've answered some common questions about your diesel particulate filter (DPF), including what it is, DPF delete and much more.

We’ve answered some common questions about your diesel particulate filter (DPF), including what it is, how it works, DPF burns, DPF warning lights, DPF delete and the legalities, DPF cleaning, DPF failure and more.

If you’ve got a later model diesel four-wheel drive, chances are, it’ll be equipped with a Diesel Particulate Filter (DPF). There is a lot of confusion surrounding the system; from how it works to what it does to if you can delete it and how much the fine is if you do.

We thought we’d knock together this write-up for you and answer all the questions you’ve ever wanted to know about the DPF system. So buckle up and grab a hold of the Jesus bar, as this is a pretty deep rabbit hole!

What is a diesel particulate filter (DPF) and how does it work? 

What is a DPF?

The overarching question – what is a DPF? To put it as simply as possible, it closely resembles a muffler somewhere along your exhaust system. It contains a filter element, that filters out diesel particulates (not just a tricky name) and often a catalytic converter. They look a lot like petrol catalytic converters, however, they’re adorned with sensors and actually catch particulates from your exhaust – then they burn them off.

How does a DPF work?

How a DPF works is a completely different kettle of fish to the petrol catalytic converter. Aside from physically capturing diesel particulates, the DPF stores them until the vehicle’s exhaust reaches a set temperature, and the vehicle can then burn them off to their most inert properties. Doing happy laps of Newtown is not going to be enough to get your exhaust to an appropriate burn-off temp. Think sitting on 100km/h for 20 minutes instead.

With this in mind, and with more and more diesel four-wheel drives being relegated to grocery-getting and school duties, many manufacturers are opting for an automated burn-off cycle, where the ECU will increase temperatures with fuel loading and other tricks. This forces the engine to undertake a ‘DPF regen’. With ongoing issues with diesel particulate filter systems on ‘city-based’ four-wheel drives, some manufacturers (read: Toyota) are even including a ‘DPF Regen’ button so you can manually control it.

What is a DPF burn-off/regeneration/regen?

There are a few different ways in which a diesel particulate filter burns off the captured material, otherwise known as a regeneration/regen.

Passive DPF burn

All DPF-equipped vehicles, once they’ve reached a certain temperature within the exhaust system, will burn off the matter caught in the DPF. The temperature reached is enough for the particles to be burnt off to ash, and this clears the DPF. This will most often happen on longer drives and is specifically how a DPF system is supposed to work.

Manual (active) DPF burn

If you’re more likely to do short hops to work, pick the kids up from soccer or get the groceries, some manufacturers have added a manual diesel particulate filter burn-off button. This essentially forces the vehicle to heat up quicker and begin a burn straight away. This is done by injecting raw fuel into your exhaust to increase temps high enough within the DPF to burn the matter out effectively, or ‘regen’. 

Undertaking a manual burn-off will allow you to do it on the way to work instead of automatically initiating a burn-off cycle while you’re sitting out in front of the kid’s school, pluming smoke everywhere.

Automatic DPF burn

The auto burn-off is essentially the same as the manual burn-off, except that your fourby will undertake a burn-off once the DPF is ‘full’, possibly in less than ideal conditions (like sitting in traffic or the shed once you get home). The DPF system has a bunch of sensors that monitor temp and amount of flow and will initiate a burn-off without you being much the wiser when it needs to.

Chances are you won’t notice the burn-off, but whoever’s sitting behind you will probably see the white plume of smoke your fourby starts blowing.

Why does the DPF do this?

Thinking back to how your diesel particulate filter system works, it’s capturing the nasty semi-unburnt matter (think soot) that would normally be dumped out of your exhaust. As it captures these particles, they get stored or caught against the filter. Over time, this builds up, and to get rid of this material, the exhaust system burns them out, cleaning the filter and breaking the particulate matter down into its most inert forms.  

Why has my DPF warning light come on?

The most common cause is that your filter is getting loaded up, and your vehicle needs a burn or regeneration. So, as soon as you can, get out to the highway and cruise for around an hour. Shifting your vehicle into second and revving the crap out of it won’t work; specific conditions need to be met before your filter will regenerate.

If the light goes out after you run up the highway, this is a best-case scenario. If not, you’ll need to visit your mechanic or dealership so they can plug it into the diagnostic process and attempt to force your vehicle to do an aggressive regen onsite.

Still didn’t work? You may need to look at getting it cleaned. More about that a bit further down!

What is DPF delete? Is it legal? What are the consequences?

What is a DPF delete?

The most common modification you’ll see to the DPF system is the DPF delete. Essentially, this entails the removal of the DPF unit from the exhaust and replacing it with a piece of straight pipe. Modifications also need to be made to the ECU on the four-wheel drive to ‘switch off’ the DPF system from the computer’s side so it won’t throw codes or live life in limp mode. There are sensors for the DPF that monitor flow, pressure, and temperature to indicate when the ECU should do a regen. If there’s no longer a PDF, there’s no need to regen, right?

Why would you do it?

The argument for a DPF delete goes like this: it removes the need to service the DPF and removes the possibility of the DPF failing, ‘possibly’ causing engine damage, or burning a hole in your wallet when you need to replace it (however, we’ve not heard of a DPF failure causing engine damage). That said, a DPF that has failed will throw error codes, drop you into limp mode, and will need to be replaced.

From a performance perspective, the delete reduces backpressure, so you get a slight increase in power, and you also do not have the gradual reduction in power as the DPF becomes clogged up before a regen. Most folks who rave about DPF deletes giving them ‘huge power gains’ will have it done when they’re getting their vehicle tuned, so it’s a bit of a misnomer.

From an economy standpoint, deleting the DPF will increase your economy, as we said above, it injects raw fuel into your exhaust to complete the regen. There’s also the bit where if your four-wheel drive is becoming sluggish due to a half-full DPF, you’ll bury the right foot further to maintain your normal driving style. But, more about the ‘economics’ of a DPF delete next.

Is a DPF delete legal?

Okay, so the $22,000 question: is it legal, and can you get fined for deleting the diesel particulate filter? The short answer is, yes you can get fined, and no, it’s not legal. We had a yarn with the NSW Environmental Protection Agency a few years back, and they confirmed it is absolutely illegal because you’re screwing with the pollution gear on a vehicle.

How much is the fine for a DPF delete in NSW (similar around Australia):

The owner/user of a motor vehicle must ensure that any anti-pollution device that has been fitted to the motor vehicle has not been removed under the Protection of the Environment Operations (Clean Air) Regulation 2010. The regulation waffles on a bit more than this but essentially says you can’t modify or delete any anti-pollution device, and if you do get caught, an individual will cop a maximum of 200 penalty units and 400 penalty units for a company.

The last time we checked, one penalty unit in New South Wales was equal to $110, so this means you as an invidiual could potentially cop a fine of $22,000. If your mechanic is brave enough to go ahead with this, they could cop a fine of $44,000.

Considering the fines, you’d be better off leaving it on there and spending that money on diesel. The question this begs, is how long would you need to drive your fourby for the economy you’d gain from the delete to outweigh the fine … probably close to 300 years.

DPF cleaners and additives

What do DPF additives do?

There are more than a few options available marketed as ‘fuel additives’ to assist in diesel particulate filter regenerating and keeping your DPF alive longer. They supposedly achieve this by reducing the temperature the soot (read: particulate matter) needs to reach before it begins to oxidize and burn off – essentially allowing your DPF to do its thing sooner and more efficiently. Most of them increase the cetane rating of your fuel a touch and also work as injector cleaners, too. There’s not really any great reason not to lob a can through your tank every so often.

Do DPF cleaners actually work?

The jury is still out on this one – with some screaming snake oil, while others saying it works a treat. So, which is it?

Our thoughts on this one are twofold. On the one hand, they assist with the diesel particulate filter burning off sooner and more efficiently, and they help keep the rest of the fuel system (injectors and tank) clean. That said, your DPF should technically automatically regen itself, so does it really need to be made ‘more efficient’?   

On the other hand, the filter ‘mesh’ (for want of better words), has a temperature and burn-off limitation. Over time, they will flog out, similarly to the petrol catalytic converters. It’s certainly possible that the additives may reduce the lifespan of the filter material.

Most additives on the market for DPF cleaning purposes suggest being run through a tank of fuel every 5,000km or so, so it’s probably a wise idea to throw one through every so often.

DPF FAILURE

How can a DPF fail?

As we’ve discussed throughout this whole article, your diesel particulate filter can and will fail. This is by not regenerating often enough, or regenerating too often, and too hot, and destroying the innards of the DPF. The filters in the DPF have a lifespan, so at some stage, you will need to have them replaced. Whether that’s in 12 months or 20 years’ time depends on how it’s treated and how the vehicle is driven, as we talked about previously.

What does it cost to replace a DPF unit?

First off, make sure you’re sitting down. The average genuine DPF can be bought from your local dealership’s spare parts department for anywhere from $7000 to $15,000. Yep, really.

Now that you’ve picked yourself up off the floor, you’ll be happy to know that there are some importers of aftermarket DPFs, which will run you between $900 and $1400, depending on the model. As with many things, the aftermarket is often cheaper. You’d be forgiven for going non-genuine when they want more than what your 4X4 may be worth.

Can a DPF failure cause engine failure?

The big question is, can a failed diesel particulate filter cause engine failure? Not specifically, no. The amount of backpressure increases through your exhaust as the DPF gets full and puts a touch more strain on your turbo and engine components; however, it is nothing more than an average trip out to K’gari.

Interestingly, if you’ve not already put two and two together and gotten 18, this is why modern vehicles have a limp mode. Sure, it’s a pain in the arse when you have an issue, and you’ve got to limp back to a mechanic, but chances are it’s saving you doing damage to your fourby.

At the end of the day…

Aside from how much of an expensive pain in the bum diesel particulate filters are, they’re not going away anytime soon. We’re all trying to be greener and to leave our kids a better place; besides, the specific particulates caught by the DPT have been shown to cause lung cancer. So, regardless of how you feel about your DPF, we’ve all got to live with them into the future.

Words by Wes Whitworth and Jessica Palmer.

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