DPF Regeneration: What It Is, Why It Matters & How to Perform It

Diesel engines are also known to be fuel-thrifty, especially when compared to their gasoline counterparts, in an apples-to-apples comparison.

That’s not all. Since their fuel, diesel, has an appreciably higher flash point than gasoline, these engines are also considered safer in vehicles, at least when (again) compared to comparable engine sizes running on gasoline.

So good are these engines that you’d be pardoned if you wonder why gasoline engines are very popular and generally sell more than these beasts of burden, burning diesel.

There are many reasons; however, for most people, it’s an ingrained hatred for diesel combusting engines, stemming from experiences over the years and hammered deep into their unconscious…

…the poor burning of diesel engines giving rise to fumes all over the place!

In this age of awareness and the desire to run clean, this memory of diesels on the road (bellowing thick, black smoke) back in the 80s, 90s, and a good chunk of the 2000s is all that is needed to divert one’s attention away from vehicles running on this superior fuel form…

…especially with the talk of ‘saving the earth’ being the new cool.

A series of regulations in Europe, the US, and elsewhere fixed this, starting in 2007 in the US with Diesel Particulate Filters (DPFs) that required DPF regeneration periodically.

However, trust in the diesel system was only just building up to be catastrophically shattered, a few years later (by what came to be known as ‘Dieselgate’).

However, let’s address the major issue first: how did the new regulations in the US, EU, and the rest of the world help make diesel engines run more efficiently, and importantly, inspire would-be users to once again consider them?

Diesel Particulate Filters & the Beginning of Trust…

The various regulations around the world involving diesel engines had something in common: they all made Diesel Particulate Filters (DPFs) compulsory in new vehicles, starting from when these regulations came into force.

These filters, mounted on the exhaust systems of vehicles (much like catalytic converters), had the singular effect of ensuring cleaner air and, overall, lowering the carbon footprint of the vehicle in question.

It worked differently, though, and had its sights on something different, though related to the catalytic converter in that they all were interested in having cleaner tailpipe emissions and overall, lowering the vehicle’s carbon footprint.

So, what did the DPF do? What did it achieve? It’s simple.

What Does a DPF Do?

Mounted on the exhaust systems of diesel-powered vehicles, a Diesel Particulate Filter (DPF) traps soot, produced from the diesel combustion process.

Instead of belching out thick fumes all around as it is driven (or operated), this soot is trapped by the DPF, and remains there till what is called ‘regeneration’ happens.

Broken down into three parts, the regeneration of the DPF is the active burning of the trapped soot in the DPF, which is the byproduct of combustion. This soot is burnt into harmless ash by heating the exhaust temperature to appreciable levels, usually through sustained high RPMs.

This happens in one of three ways: passive, active, or forced.

1. Passive DPF Regeneration

Passive DPF Regeneration happens as you drive your diesel-powered car or truck on your normal business, usually on the freeway.

This is how it pans out: at freeway speeds, usually at RPMs above 2k, the engine and exhaust heat up in a manner that raises the temperature of the particulate filter, burning the soot trapped in it to harmless ash.

The passive regeneration process happens in the background as you drive and mind your business. You’re hardly notified when it starts or when the whole process wraps up, which is why it’s termed ‘passive’ in the first place.

For passive regeneration to take place, exhaust temperatures need to reach, on average, 600 degrees Celsius (1112 degrees Fahrenheit). While this is the lower end of the spectrum, it isn’t uncommon for exhaust temperatures to exceed that during passive regeneration, especially during spirited driving, navigating hilly terrain, or driving with impressive loads onboard.

2. Active DPF Regeneration

Passive DPF Regeneration is a cool and sensible concept – except that, like all good and cool things, it doesn’t always happen when it should. This failure is often a result of not driving the vehicle at high RPMs for considerable durations.

The above scenario happens to:

• Grandma’s style of drivers who are generally very ‘considerate’ of the gas pedal and wouldn’t want to ‘hurt’ it.
• Cars/vehicles driven exclusively in city traffic where it’s impractical to get to (or keep) high RPMs.
• Articulated/heavy-duty construction/agricultural machinery, where work done and miles logged don’t usually correlate.

If you’re in any of the above scenarios, your vehicle will hardly meet the conditions for a DPF Regeneration. For a regen to happen, you’ll need to initiate one yourself.

For most makes and models, you’ll be prompted to initiate this process by an instrument cluster warning. This happens when the soot accumulation in the DPF is about 80% full.

The process of an active DPF regen is simple: drive the vehicle to operating temperature, park it on a clean, hard surface, start the engine, and flip the Regen Switch, usually on the dash (or virtually, through the fancy displays).

During the active regen process, the vehicle will run idle speeds higher than what is considered normal, raising itself periodically, through the cycle. During the process, too, white smoke may be emitted from the tailpipe.

The process is automatic and usually does not need tending or human interference once it’s put in motion. It takes an average of about 40 minutes to wrap up (at which point you get a notice to switch off your engine or the engine powers itself off to save diesel, depending on the make, model, year, and configuration).

3. Forced DPF Regeneration

If an Active Regen sounds like the failsafe of a passive, background regen, that’s because that is what it is.

However, sometimes, an active regen fails too, especially on heavy-duty agricultural/construction machinery or on vehicles that have had their particulate filters ignored for long.

When this happens (and it’s more frequent than you imagine), the affected vehicle is usually in limp mode, operates at a quarter of its power, or generally behaves inconsistently.

This is where a forced DPF Regeneration comes in and is needed.

With a Forced DPF Regen, a capable scan tool is hooked to the DLC of the vehicle in question, and the command is given for the vehicle to enter into Regen and do its thing.

This process usually takes about an hour and can cost anywhere from $300 to $500 if outsourced to a shop or dealership.

It’s also the last resort for DPF clearing issues. If this fails (it hardly does, anyway), a new Diesel Particulate Filter is usually recommended.

So, for emphasis, why all the DPF stress? Why does a diesel regen need to happen in the first place?

It’s simple, and all boils down to making this earth we call home more livable for all of us.

For a comparison of these DPF reset types, see the article: Passive vs Active vs Forced DPF Resets Explained Simply.

Why a DPF Regeneration Happens in the First Place…

DPF Regens, when they fail, are a major source of worry for both the operator of the machinery and the owner. This is because fixing the issues usually requires hard-earned money leaving one’s pockets, not to mention lost man-hours when the vehicle was in limp mode or was only working at half-quarter capacity.

Again, the challenges don’t stop there; regeneration is only a part of the equation. After all is said and done, the Particulate Filter needs to be replaced (after running its course), which is usually an added expense, an expense that wasn’t there pre the DPF era.

Seeing that the introduction of the DPF (and the associated technology) has caused more ‘harm’ and ‘grief’ to those who must use such vehicles as it’s compulsory now, why are new vehicles still mandated to come with them? What’s the catch?

It’s simple, and quite straight to the point…

As already mentioned, the presence of a Diesel Particulate Filter (DPF) and the subsequent DPF regeneration that must periodically happen are the reasons (and difference) between a black smoke-belching diesel engine and a clean-running one.

Without such regulations, our roads, especially in such places as California, would truly be a mess, with pollution that would rival the output of a 19th-century European factory site.

This, as you know, is better imagined than lived in.

However, there are some special groups of folks who believe that they know better. These folks, spanning local mechanics, users, and even manufacturers, do all they can to undermine the system and take us all back.

One of such bad examples is Volkswagen.

Volkswagen’s ‘Dieselgate’ & the Sad Aftermath for Diesel Engines

Starting circa 2015, Volkswagen began equipping its diesel-powered vehicles with a cheat system to beat diesel regulations. How this happened is simple: the diesel engines in most Volkswagen diesel-powered vehicles at the time, including the Beetle, Jetta, and Passat, were designed with a computer that easily detected when a vehicle was being tested.

The ‘onboard’ computer achieved this by a myriad of sensors that could easily figure out when a vehicle was on the ramp (by monitoring engine operation, speed, air pressure, and the position of the steering wheel).

Once this elaborate computer figured out that a test was in progress, it reduced engine power, and the vehicle in question passed emissions tests, in flying colors. Once down the rig and on the roads, it self-deactivated and everything went back to ‘normal’.

The outcome? Emissions and general pollution levels that were more than 40x what was legally allowed in the US!

Now, despite the advancement of technology and the introduction of DPFs to modern diesel vehicles, the general distrust remains: the unsaid issue now, at the back of every skeptic, is: what manufacturer is actively trying to cheat the system now?!

FAQs

Contained below are some Frequently Asked Questions (FAQs) that will clarify some concepts you may have missed.

Enjoy.

Summary

Diesel Particulate Filter Regens are the new reality of diesel vehicles today, even if manufacturers like Volkswagen actively tried to undermine collective trust in the technology.

With the process, DPFs easily burn out collected (and trapped) soot via sustained high RPMs. What this ensures is less tailpipe emissions, less carbon footprint, cleaner air, and generally, a greener earth for us all.

Diesel Engines aren’t the mess they were, pollution-wise, decades ago; all thanks to functions such as the DPF reset.

However, as for less-than-honest players like Volkswagen, only time will tell.

Addendum: DPF Regeneration for Modern Heavy-Duty Trucks & Construction Machinery

DPF regeneration is needed not only for cars and SUVs, but also for heavy diesel agricultural and construction machinery.

Unfortunately, when it comes to forced regeneration, most traditional OBD II scanners are helpless (partly because they aren’t designed to scan heavy-duty vehicles and partly because, most of the heavy duty trucks use a DLC that is radically different from the regular OBD II compliant ports we all know and use (cue Cat-9 or DIESEL-6/9).

If you’re that farmer or construction yard owner who doesn’t appreciate shelling out $500 for a DPF regeneration by the dealer’s hand (or a private mechanic’s), then you should consider taking a close look at the Ancel HD3600.

The HD3600 is a heavy-duty scanner that is so easy to use that you’ll be running your regens right after you unbox, even as a complete novice!

The best part? The scanner pays for itself right after the first regen service. Does it ever get better than that?

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