Soot Levels Under 5%: Is This Normal?

Hello everyone,

My Passat B6/3C (manufactured in 2006, 208,000 km, BMP engine) regenerates every 350 km, seemingly based solely on mileage . I have been driving this vehicle for 1.5 years, and for the past year, I have practically observed all regenerations using VCDS. (The diesel particulate filter installed from the factory is catalytic - meaning it does not require an additive.)

The loading coefficient (from measurement block 068, "Particulate filter, exhaust values II") was always below 5% before regeneration - and naturally 0.0% afterwards.

The regeneration process always runs smoothly, with consistent temperatures and duration. It takes approximately 10 minutes, reaching temperatures of around 800°C before the exhaust turbocharger and approximately 660°C inside the particulate filter.

Differential pressure: 0 at engine start, 5 at idle, 50-80 during normal operation, and 100-130 under heavy load, all within the normal range.

According to the VCDS tooltip, a target value of up to a maximum of 40% is expected for the soot loading coefficient ("regeneration begins during driving operation from 40% onwards"). Therefore, I find the low soot loading in my case - always below 5% - very surprising.

The route mix is: minimal city traffic, more frequent highway sections of 35km each, and occasional long-distance stretches. The regularity of the regenerations - strictly every 350km - seemed reasonable to me, considering the low soot load. (I thought that there was probably also a regeneration based on mileage, in case the soot load doesn't trigger one.) By the way, I use regular diesel, no "premium" or "ultimate" or anything similar.

If I understand correctly, the soot level is also a theoretically calculated value (using differential pressure and/or temperature sensors, or similar), since the actual soot level cannot be measured anywhere.

Is it conceivable that a consistently low soot level of less than 5% could be achieved? Or is that actually not possible, and is my engine system measuring (or calculating) something incorrectly?

I would be interested in hearing your opinions on this - thank you in advance.

During my research before asking my question, I found Rainer's explanations in https://community.dieselschrauber.org/en/viewtopic.php?t=27763&start=24 to be interesting.

Quote:

... the engine control unit calculates the amount of soot based on the differential pressure in the respective operating condition. However, since the ash mass increases with each regeneration cycle, the differential pressure values generally increase over time. Based on this, along with the mileage and the amount of fuel consumed, it is possible to estimate the ash mass in the filter. Based on my experience, the ash mass reading tends to be more of an "estimated value" than an "actual measurement." I had my DPF removed after approximately 80,000 km, and although the ash mass calculated by the engine control unit was within the usual expected range, the filter itself was practically empty. I mean, it's difficult to predict how much ash is actually inside, depending on the engine oil used (additives/oils that produce less ash or are less ash-prone), the wear condition of the engine (high oil consumption or very little), the driving profile, and the fuel used.

So, the differential pressure values observed during operation have actually not increased over the approximately 1.5 years I've been monitoring them, and the amount of ash produced during that period (with a mileage of about 12,000 km) is only about 3 grams, which also seems quite low to me.

Here are the details of the engine control unit:

Address 01: Engine Control Module
Label file: DRV\03G-906-021-BMM.clb
Part number SW: 03G 906 021 NK. Part number HW: 03G 906 021 AB.
Component: R4 2.0L EDC G000SG 9354
Revision: --H02--- Serial number: VWZCZ000000000
Encoding: 0000072
Operating number: WSC 05311 000 00000

Hi,

You have completely overlooked an important connection. There are two loading values. At least, that's how I know it from the CR engines (see SSP 403).

One is derived from the driving profile, the exhaust temperature sensors, and the lambda sensor.

The other value is determined based on the flow resistance, which is derived from the differential pressure, the exhaust temperature sensors, and the mass airflow sensor.

And the one with the highest value initiates the active regeneration. It's almost always the one with the driving profile. But it seems you're only observing the single load value derived from the airflow. Or maybe the MSG only displays that one; I'm not sure how it was handled in the PDs.

If neither of the models is applicable, there is a fallback option: a regeneration system based on distance traveled, which activates when a certain distance threshold is reached.

Quote:

According to the VCDS tooltip, a target value of up to a maximum of 40% is expected for the load factor ("regeneration begins during driving from 40%").

Field regeneration (driving operation) typically starts at 20 grams, while the limit for service regeneration varies depending on the model, but is approximately 40 grams.
Where did you get the percentages, and what are they supposed to represent?
If they are indeed grams, I would be surprised if the values were so different for PD engines compared to CR engines.
hg
Herbert.

I also own a Passat 3C BMP, but it's one year younger and has 300,000 km on the clock. I had the filters flushed around 200,000 km. I also primarily drive long distances, and the DPF regenerates reliably only through driving, but every 390 km. (I record the mileage, and I can say that the last six regeneration cycles totaled 2342 km, which averages to 390 km and is very consistent).

I haven't checked the percentages in a while, but they were also well below the limit displayed in VCDS. I don't remember the exact numbers, but I can check them again sometime soon. Unfortunately, it regenerated this morning, so I won't be able to check it until the end of next week.

Greetings.
Guste.

Hello Roger, Herbert, and Guste,

Thank you for the answers, they were all very helpful. Here are my responses to the questions:

Roger: Thank you for pointing out SSP 403, I have now reviewed it. While my original statement ("using a differential pressure and/or temperature sensor or similar") allows for two loading models, it appears that the engine electronics in my (older) engine only assume one loading model.

Because, in the case of PD engines with a catalytic diesel particulate filter, it appears that there is no explicit mention of two loading models (at least not in the corresponding SSP 336), but rather only:

Quote:

The engine control unit infers the loading status of the filter based on the flow resistance of the filter. A high flow resistance indicates that the filter is likely to become clogged. The engine control unit then initiates the active regeneration process.

I couldn't find a second load value anywhere in the data blocks either - perhaps others with similar engines can check to see if I've missed something. (But I don't think I have.)

However, the SSP 403 document you mentioned explicitly refers to two different loading models for CR engines.

Quote:

The soot loading of the particulate filter is calculated using two pre-programmed loading models in the engine control unit. One loading model is determined from the user's driving profile, as well as from the signals of the exhaust temperature sensors and the lambda sensor. Another soot loading model is the flow resistance of the particulate filter. This is calculated from the signals of the exhaust pressure sensor 1, the exhaust temperature sensors, and the mass airflow sensor.

Herbert:

Quote:

Field regeneration (driving operation) typically starts at 20 grams, and the limit for a service regeneration varies depending on the model, but is approximately 40 grams. Where did you get the %, and what percentage of what are they supposed to be?

As mentioned, the percentage value for the loading is the "loading coefficient" (in percent) from measurement block 068, "Particulate filter, exhaust values II." I can't really answer what the percentage refers to; I lack the expertise for that. Perhaps others here can contribute more information. I personally assumed it was a percentage of a theoretically calculated maximum loading (which, however, is not explicitly given in grams).

The quote I mentioned for the maximum target value (the percentage given in document MWB 068) comes from the tooltip in VCDS, which further states: "Regeneration begins during driving operation starting from 40%."

Based on the feedback I've received so far and my own observations, I conclude that my engine has been regenerating solely based on the mileage model, and not the load model, during the observation period (as I mentioned, over a year), because the load coefficient is consistently displayed as being below 5%.

Guste: We actually have a vehicle from a similar year with the same engine (BMP), but with slightly different mileage (yours has 330,000 km, mine has 210,000 km). Mine used to regenerate regularly every 390 km (the load coefficient was always below 5 percent, usually much less), but for many months now it's been regenerating every 350 km (I suspected that the reason for the change was that the kilometer-based model shortens the intervals somewhat with higher ash content, and my diesel particulate filter already has a relatively high ash load).

It would be very interesting to know what percentage values of load you – or, of course, others with a similar/identical engine – are seeing in measurement block 068, between regenerations (I understand that this is still ongoing...). Thank you for the offer.

Because sometimes I fear that these minimal percentages I'm seeing are almost too good to be true.

Thank you again to everyone, and best regards.

Hi,
My mistake regarding the percentages (please forgive me). The values from the data sheets are as follows for the PD motor. If I set the 20g soot load for the CR as 40%, then 100% corresponds to a mass of 50g, which is the read-out limit for overload in the R4 CR.
I have also observed that regeneration starts significantly earlier. The trigger is the calculated value. I have already seen deviations of as much as 10 grams (which would be 20% in your case).
As long as the ash content doesn't reach its limit and the pressure difference isn't excessively high, you shouldn't encounter any construction-related issues here.
Your problem is the leaks and the increasing oil consumption.
hg
Herbert.