DPF Problems: Common Issues and Solutions

Hello everyone,

I'm receiving an increasing number of reports about problems with the DPF (Diesel Particulate Filter).

Currently, a friend of mine owns a Renault.

He drives a company car, and she uses it for any personal trips possible. She has a Renault, which is a diesel only because she needs to tow a caravan on vacation. Otherwise, she drives 3 km to take the children to school and 2 km to go shopping, and often doesn't drive at all. The DPF is constantly getting clogged and doesn't regenerate (when would it?).
Advice from a friendly source: Once or twice a week, for 20 minutes, fully accelerate on the highway.

But she lives 20 minutes away from the nearest highway, and she never drives at full speed.

The friendly representative has now told you that the warranty has expired, and that you will eventually have to pay for the DPF replacement every quarter.

I suggest we collect stories here, because it's inevitable that people will want manufacturers to reimburse them for the exorbitant costs associated with DPF (Diesel Particulate Filter) replacements.



And then there was a female colleague who sold her Peugeot after the second DPF replacement (at 120,000 km) because it became too expensive for her in the long run. It was regenerating normally, but when the DPF is clogged with ash, that's it! Incidentally, the pressure sensor in front of the DPF was unnecessarily replaced, but at a charge, because the DPF couldn't possibly be clogged again... but it was!

garth.brooks wrote:

... I'm receiving an increasing number of reports about problems with the DPF (Diesel Particulate Filter).

Not just with you...

Quote:

Currently, a friend of mine owns a Renault. He drives a company car, and she uses it for any personal trips possible. She has a Renault, which is a diesel only because she needs to tow a caravan on vacation. Otherwise, she drives 3 km to take the children to school and 2 km to go shopping, and often doesn't drive at all. The DPF is constantly getting clogged and doesn't regenerate (when would it?).

Typical short-distance driving profile (school, daycare, bakery, butcher, and home). Every car should be able to handle this without any issues. However, DPF vehicles can't... It's quite strange.

Quote:

Advice from a friendly source: Once or twice a week, for 20 minutes, fully accelerate on the highway.

Yes, unfortunately, it has to be this way -> https://community.dieselschrauber.org/en/viewtopic.php?t=2171&start=74

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But she lives 20 minutes away from the nearest highway, and she never drives at full speed.

So, it's actually an economically efficient driving style. The DPF doesn't like that very much .

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The customer service representative has now told you that the warranty has expired, and that you will eventually have to pay for the DPF replacement every quarter.

I'm already looking forward to those jokes...

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... And then there was a female colleague who sold her Peugeot after the second DPF replacement (at 120,000 km) because it became too expensive for her in the long run. It regenerated normally, but when the DPF is clogged with ash, that's it! Incidentally, the pressure sensor in front of the DPF was initially replaced unnecessarily, but at a charge, because the DPF couldn't possibly be clogged again... But it could!

These problems are absolutely independent of the manufacturer. Unfortunately, in my opinion , the DPF technology is not yet advanced enough to be considered suitable for everyday use. A mandatory DPF would therefore be the death of DI technology. But that's what our politicians want. Only in Germany will the DPF become mandatory, while in other EU countries, it doesn't matter (so far).

I also see a huge wave of problems coming for manufacturers: Apparently, there are a lot of people who only drive their diesel cars for short distances. Diesels were never really suitable for that, but with a DPF (Diesel Particulate Filter), it's doubly problematic.

Here's a rough estimate:
The regeneration process itself takes at least 10 minutes, and at most around 20-25 minutes.
Of course, this only starts when the engine is warm, so depending on the ambient temperature and driving style, it might take another 10-15 minutes.

If one were to immediately drive onto the highway/country road after starting, it would then take at least 20 minutes to successfully regenerate.
Realistically, it's probably more like 30-35 minutes, assuming ideal traffic conditions.

That means that even for people who commute 30 km to work every day, the intervals might be shortened.

This doesn't only put a strain on the DPF itself: In the above-mentioned case, it's the systems with additives, where a relatively large amount of ash remains after regeneration. The ash accumulation caused by incomplete regeneration initially leads to filter clogging, resulting in the complications described (replacement of the DPF/sensor).
In the common systems without additives used here, a higher oil dilution is more likely, as the higher temperature level necessary for oxidation must be achieved through a suitable injection strategy. This involves injecting fuel very late after top dead center, which, due to the wall film, dilutes the oil.

Translation: Frequent oil change intervals / unclear long-term durability / increased fuel consumption (especially during a time of climate crisis).

DPF systems are only suitable for long-distance driving. For vehicles that are not typically driven in this way (mid-size/compact cars), there will be widespread problems. This is due to the laws of physics and is therefore independent of the manufacturer.

DieselWiesel wrote:

Here's a rough estimate: The regeneration process itself takes at least 10 minutes, and at most around 20-25 minutes. Of course, this only starts when the engine is warm, so depending on the ambient temperature and driving style, it might take another 10-15 minutes. If one were to immediately drive onto the highway/country road after starting, it would then take at least 20 minutes to successfully regenerate. Realistically, it's probably more like 30-35 minutes, assuming ideal traffic conditions.

It's a bit of a mixed bag. Normally, the regeneration process happens very quickly. Once the temperature at the filter is reached, the back pressure decreases to almost zero within a few hundred meters. The problem is reaching that exhaust gas temperature. The main issues are things like faulty EGR valves, and similar problems. With the additive systems, the problem is often defective additive pumps.

I need to provide an example from my engine. Shortly after a cold start (when the engine management system indicates "now I'm running freely"), I see the temperature rising according to the display. At a constant speed of 50 km/h, the temperature at the filter reaches 450°C after just 2 km. When driving uphill, you can watch as the display increases by 25°C every 5-10 seconds.

I believe that all these problems with vehicles that use an additive are due to a defect. It's almost impossible to drive such short distances without the additive not being fully burned off. Considering that, even with slow driving in city traffic, the filter only slowly reaches its saturation point after over 500 kilometers.

"With catalytic DPFs, there are indeed more problems. Once the filter becomes clogged, almost nothing flows through anymore, because the platinum and barium oxide, which are the catalytic elements, are covered by soot. In this case, temperatures above 650°C are needed to burn off the soot, which is the same as if there were no catalytic coating."

The most important thing is the right type of engine oil, and taking it for a longer drive of about 20km every 500km. Now everything is working properly again, and the catalytic converter is no longer clogged.

"I don't see ash as much of a problem. I always used 10w60 oil from Shell, which isn't exactly low-ash oil. After 80,000 km, the filter burned clean with hardly any extra load, almost as if it were new. However, every 80,000 km, Peugeot would replace the filter for free, but I had to pay about 100€ for the additive. That's why I don't understand why the lady had to pay for everything herself. The workshop was incompetent again. If they had burned off the filter on the highway or in emergency mode, they would have seen that it was soot containing too little or old additive, which prevents the catalytic effect, just like a completely soot-covered catalytic filter."

@Aaron:
Yes, you're probably right. I should add that my example refers to the additive-free solutions offered by German manufacturers.
The exothermic reaction in many solutions is triggered by a catalytic converter (cat), rather than being caused by a coating on the diesel particulate filter (DPF), but this is just a side note, as the effect will be the same whether it occurs on the cat or the DPF.

In my opinion, it's not so much the engine oil that contributes to soot formation, but rather the 'normal' soot generation that occurs depending on the driving profile.

The back pressure itself is only an indirect measurement and is used only for diagnostic purposes (in this case, I can only provide information for additive-free systems). Otherwise, a loading model is used.

Anyway, for additive systems, I believe the problems are more likely to be limited to the DPF system itself, specifically the filter and sensors, the additive pump, etc.
For the others, I predict more likely secondary effects due to the oil dilution, as described below.

DieselWiesel wrote:

Yes, you're probably right. I should add that my example refers to the additive-free solutions offered by German manufacturers. The exothermic reaction in many solutions is triggered by a catalytic converter (cat), rather than being caused by a coating on the diesel particulate filter (DPF), but this is just a minor detail, as the effect will be the same whether it occurs on the cat or the DPF. The back pressure itself is only an indirect measurement and is used only for diagnostic purposes (in this case, I can only provide information for additive-free systems). Otherwise, a loading model is used.

Okay, most of the filters from Mercedes-Benz and the Volkswagen Group are manufactured by Fauricia, and they were developed by Renault in 2003.

In the pre-catalytic converter stage, the hydrocarbons are burned, which is evident during transient operation. You can observe this by noting that the temperature at the turbocharger decreases, while the temperature after the catalytic converters continues to rise.
"That's exactly the problem: the catalytic filter starts reacting at 450°C if it's not completely clogged, but if it's heavily loaded, this only happens at much higher temperatures. And reaching those higher temperatures takes longer and consumes a lot of fuel. You mentioned oil dilution, and even with the additive versions, the second injection occurs up to 120° after the crankshaft's top dead center (TDC) specifically to oxidize the diesel particulate filter (DPF)."

Back pressure is correct, but the most important thing is the conversion using the values of exhaust gas temperature and air mass intake.

In the "autoblöd" magazine from March 16th, there's a small table printed that shows, for example (according to the manufacturer), what to do if the filter is clogged.

Nissan, for example, states that you should drive for at least 30 minutes at a minimum speed of 80 km/h .

So, the warning light is on.

Immediately stop the car. Pick it up at night and then, at 4:00 AM, drive 40 km along the highway.

In my opinion, we should try to modify all of these vehicles, as they don't seem to be ready for everyday use yet.

@Aron,

You're mixing up the temperatures in catalytic systems a bit.

I am now referring to the manufacturer HJS, as I have found the best information here. However, I assume that the principle remains the same for all catalytic filters.

The catalytic reaction begins at an exhaust gas temperature of as low as 200°C.
If the filter is so clogged that, as you write, the catalytic element is completely blocked, and the filter acts like a less effective aftermarket filter, then the self-regeneration process begins at just 450°C. This is, for example, the exhaust temperature of a racing filter, which should not be dropped below this level, as the filter would then be completely passive.

If the 650°C you mentioned were correct, you wouldn't be able to regenerate the DPF.
You won't achieve these high exhaust temperatures, even on the highway, within a 15-minute period. A 64 horsepower naturally aspirated diesel engine will likely only reach these temperatures during maximum speed or full throttle driving in lower gears, and only over a longer period.

The 850°C exhaust gas temperature is solely used to ignite the soot particles. Once these particles ignite, the regeneration process will only end when there is no fuel, or no oxygen (engine off).
That's why the prescribed regeneration times are in place.
Actually, the principle is the same as the ovens you have at home.

If I could maintain an exhaust gas temperature of 850°C throughout the entire regeneration process, I could potentially switch back to a V8 gasoline engine.

Nevertheless, regeneration in short-distance travel is a major problem.
(See the article in *The Times*, which has already been linked here.)

In the USA, the diesel particulate filters (DPFs) of large diesel vehicles are also actively regenerated.
Primitive, but effective:
If the warning light for the regenerative braking system illuminates, I must stop the vehicle!
The engine is switched to regeneration mode and idles at approximately 2500 rpm until the required exhaust gas temperature is reached.
Since these are older diesel engines with PLDs, I have no other way to initiate the regeneration process. In the USA, DPFs were also retrofitted. Of course, an engine overhaul (with a different camshaft, etc.) is not planned.

So, if nothing else works, in the future we will have recovery stations in addition to the emergency stopping areas, not only on highways but also on country roads and, above all, in the city.
Here, the vehicles are then idling with the engine running at 3500 rpm or more (or is it better ).

Best regards, Jochen.

Jochen_145 wrote:

@Aron, You're mixing up the temperatures in catalytic systems a bit. I am now referring to the manufacturer HJS, as I have found the best information here. However, I assume that the principle remains the same for all catalytic filters. The catalytic reaction begins at an exhaust gas temperature of as low as 200°C. If the filter is so clogged that, as you write, the catalytic element is completely blocked, and the filter acts like a less effective add-on filter, then the self-regeneration process begins at just 450°C. This is, for example, the exhaust temperature of a racing filter, which should not be dropped below this level, as the filter would then be completely passive. If the 650°C you mentioned were correct, you wouldn't be able to regenerate the DPF.

The catalytic coating process works, under optimal conditions, at 200°C. In practice, it's difficult to achieve. Measure the exhaust temperature on a TDI with an exhaust temperature gauge; it's almost impossible to get below 200°C after the catalytic converter, even during city driving. But why do these things constantly get clogged?

Looking at the manufacturer's specifications, the catalytic converters activate at temperatures above 650°C. The catalytic component is only used for natural regeneration during driving.

"Reaching 650°C is quite easy with the second injection stage. Moreover, the exhaust temperature is even higher on the highway at maximum speed. I was initially surprised and thought my gauge wasn't working correctly, but you can expect temperatures of 700-800°C when running at full throttle for 5 minutes."

The forced exhaust gas temperature during regeneration is usually not critical for the turbocharger. At most, 10% of the total amount of diesel fuel (which is injected during the post-injection process) is vaporized in the cylinder. This vapor ignites in the 400°C hot catalytic converter, causing a momentary but significant temperature increase. Theoretically, it would be possible to use the software to "burn off" the filter at 1000°C if necessary, without significantly stressing the turbocharger's temperature limits.

With the additive, the soot burns off at 450°C during regeneration, which is just above the exhaust temperature achieved with EGR at 100 km/h. In catalytic systems, the soot must be burned off at higher temperatures because, without the additive, the catalytic converter is not functional (it lacks catalytic components on the surface), and the catalytic regeneration apparently did not occur naturally.

Yay!
Then diesel vehicles will soon be as attractive again as they were before the diesel crisis.
Then they succeeded in expanding the culture of compulsive consumption. Even today, I can't even guess what flimsy arguments will be used to justify the introduction of future AGR, DPF, and similar derivatives. The media are likely the means to an end. We could bet on what nonsensical thing will be hyped up next. Ideally, we should all be driving around in 3.5-ton armored vehicles, because international terrorism with its bombs lurks everywhere.

Ground-level ozone hysteria -> Agricultural emissions are the cause.
Fine particulate matter hysteria -> DPF (Diesel Particulate Filter) is coming, and suddenly, EGR (Exhaust Gas Recirculation) is contraindicated!
CO2 hysteria -> EGR and DPF are contraindicated! The logical consequence to still get decent performance from my 1.6-ton vehicle is increased fuel consumption!

Here, one could initiate a fundamental discussion.

Either, and in the most favorable scenario, it's all just a political performance, where narcissistically disturbed talkers (our so-called politicians) have nothing better to do than create something like this, lacking any real purpose, driven by envy and, of course, boredom.

According to the dystopian view, the stability of our cultural sphere is based on functioning and consumption. One depends on the other, and both should be maximized as much as possible. The zeitgeist and the media dictate this conditioning (through advertising and modern work culture, as well as rewards). If all of this is not enough, it can be artificially amplified, for example, through staged incidents like those involving diesel particulate filters in cars, or through wars like the one in Iraq. If the 'diesel particulate filter' of our Western societal system becomes clogged despite maximum consumption and the aforementioned coercive measures, then we can look forward to a 'regeneration measure' involving the developing world, in order to restart the clogged cycle of function and consumption.

In the first case, I wonder why we, who used to thoroughly bully those politicians on the playground when we were children, now feel compelled to unconditionally recognize them as credible authorities. In the second case, I fear I have no other recourse than a cultural revolution.

Have a nice weekend.

Please measure the exhaust temperature on a TDI engine. An exhaust temperature below 200°C after the catalytic converter is practically impossible, even during city driving, but why do these things constantly get clogged?

Hello Aron, you're absolutely right, there's no question about that.
In practice, I can regenerate it at 200°C! The fact that I can't reach that temperature is a different problem.

Looking at the manufacturer's specifications, the catalytic converters activate at temperatures above 650°C, and the catalytic component is only used for natural regeneration during driving.

The catalytic element ensures that I reach the required temperature in the DPF.
For the catalytic converter to function properly, the temperature must be significantly above 200°C. According to HJS, this temperature is 450°C. This is the minimum operating temperature for motorsport-specific diesel particulate filters (DPFs) that do not contain a catalytic element.
This element functions like a 'lighter' and starts working at temperatures of 200°C or higher. This is where the principle of catalysis comes into play.

Reaching 650°C is easily achieved with the second injection,

Yes, that's correct. A catalytic diesel particulate filter (DPF) is used in retrofit applications, where there is no provision for after-cooling injection.

Furthermore, the exhaust temperature is even higher on the highway at maximum speed. I was initially surprised and thought my gauge wasn't working correctly, but with 700-800°C, you can expect that after 5 minutes of continuous full throttle.
Yes, that's possible with your engine calibration (didn't I see something about 130 kW or more in your profile?).
However, things look quite different with a 90 horsepower engine or a naturally aspirated diesel engine with 64 horsepower.
You can't be certain that you can drive at full power for 5 minutes continuously. This is especially true in urban areas and on country roads.
Herein lies the exact problems of current DPFs.

The forced exhaust gas temperature during regeneration is usually not critical for the turbocharger, with a maximum of 10% of the total diesel fuel (which comes from the post-injection) being only vaporized in the cylinder. This vapor ignites in the 400°C hot catalytic converter, which causes a momentary and very high temperature increase. Theoretically, it would be possible to 'burn off' the filter with 1000°C via the software if necessary, without significantly stressing the air temperature limit (ATL).

No.
Depending on the turbine construction (VTG), there are fixed, material-related temperature limits. If the adjustable vanes regularly exceed 850°C, they become brittle and will eventually break. The load caused by over-temperature is less of a factor.
'The vaporized diesel fuel will not ignite in the catalytic converter, but rather in the turbocharger, because the turbocharger is significantly hotter than the catalytic converter when the engine is warm. In a common rail (PD) engine, the fuel may even combust in the combustion chamber because it cannot be injected early enough.'
Only with CR (Common Rail) injection systems can I inject directly into the combustion chamber during the intake stroke.

But let's go back to the starting point: I was talking about aftermarket filters that don't have any of these features.

Best regards, Jochen.

Jochen_145 wrote:

But let's go back to the starting point: I was talking about retrofit filters, which don't have any of those features. Best regards, Jochen

Aaaah, I forgot to write that earlier, I was almost thinking that we were talking past each other.

However, retrofit filters have one advantage: they are less likely to become clogged compared to closed filters, although even with those, significant flow losses occur when the catalytic fleece becomes saturated with soot.

"But catalytic systems are also available in production vehicles. It's a shame that PSA is so focused on licensed technology and fees that it makes additive systems too unattractive for other manufacturers, leading them to accept more problems. (Just a note: PSA's 6-cylinder engines also use an additive system, and they now have a 240,000 km interval for the additive and filter, coinciding with the first timing belt replacement)."

It is a politically motivated decision. The required modifications to diesel engines significantly increase their purchase price compared to gasoline engines. This will result in a surcharge in the small and compact car classes that will no longer be around 10%, but will instead be in the range of 35-40%. As a result, it is no longer attractive for any manufacturer to offer such vehicles in Germany. Models like the Renault Clio dCi, Smart CDI, or Corsa CDTI will eventually no longer be available here.

Hutfahrer wrote:

It is a politically motivated decision. Due to the required modifications to diesel engines, they become significantly more expensive to purchase compared to gasoline engines. This will result in a surcharge in the small and compact car classes that will no longer be around 10%, but will instead be somewhere between 35-40%. As a result, it is no longer attractive for any manufacturer to offer such vehicles in Germany. Models like the Renault Clio dCi, Smart CDI, or Corsa CDTI will eventually no longer be available here.

Without me wanting to write about politics again (this is a technical forum!), but a large proportion of gasoline direct injection engines will also need a particulate filter from 2009 onwards, otherwise most of them won't meet the Euro 5 standard. (The working principle with stratified charge and over-rich, lean areas in the combustion chamber is already similar to the diesel principle, which is why there are the same problems .

Without me wanting to write about politics again (this is a technical forum!), but a large proportion of gasoline direct injection engines will also need a particulate filter starting in 2009, otherwise most of them won't meet the Euro 5 standard. (The working principle with stratified charge and over-rich, lean areas in the combustion chamber is already similar to the diesel principle, which is why there are the same problems .

Does the Euro 5 standard impose the same emission limits for diesel engines as it does for gasoline engines?
Or are gasoline engines then allowed to produce more soot than diesel engines? (which is something that is sometimes observed today).

DieselWiesel wrote:

... Does the Euro 5 standard impose the same emission limits for diesel engines as it does for gasoline engines?

NO.

Quote:

Or are gasoline engines then allowed to produce more soot than diesel engines?

Possible.
But it is actually true that for direct-injection gasoline engines, a limit for particle mass is required starting with EU5 standards. This would likely also mean that a particulate filter (PF) is necessary here.