DPF Issues: Golf 6 GTD - Common Questions

Hello, I'm new to this forum and I'm hoping to finally get answers to my open questions .

I drive a Golf 6 GTD with a performance upgrade from a well-known tuner. In the past, the car was modified for more power, but it then started producing excessive soot. I took it back to the tuner, who adjusted the settings to reduce soot, but only under full load. It still produces soot at higher RPMs. In short, I suspect the DPF (Diesel Particulate Filter) is faulty. After all, the DPF is supposed to prevent soot emissions.

Okay, let's move on to the first question. I often monitor my car's data via OBD Eleven, and I see the measured oxygen sensor voltage, which is always between -6 and -8, or even -9.
For me, this is a clear sign of a DPF problem. A negative value means there's nothing left inside, and the soot confirms it. However, I recently checked a comparison vehicle, a standard model, which doesn't show any soot, and it also has a measured value of -5 grams. Can anyone explain this?

I once logged my differential pressure, which was 2100 RPM in the 4th gear. According to a website (which states a range of 20-50 mbar), the pressure seems to be okay at around 30 mbar.

The car now has 176,000 km on the odometer. About 3,000 km ago, the oil consumption jumped to 0.12 liters.

"The DPF is full at 0175ml - what happens at 0175ml? Does it trigger a check engine light? It's possible that the pressure could become too high, leading to damage to the turbocharger, etc. However, I've also read from other people who have 65 grams of oil ash, and according to the manufacturer, the DPF is supposed to be clogged at 60 grams of ash. The car continues to run without problems. Has anyone else experienced this with a Golf 6 or, more generally, a 2.0 TDI CR engine?"

The OBD Eleven app has a section for initializing the particulate filter, which means resetting it. It suggests setting it to "0TKM," which means a new DPF. Let's say the car, with 240,000 km on the odometer, is telling me the DPF is "full" with 175ml.
"Can't I simply set the value to, for example, 5,000 km? The DPF probably has a crack, so there's likely nothing left inside, perhaps just some ash? Or maybe not. I'm a car mechanic myself, but despite a lot of research, I can't answer these questions."

Okay, yes, the differential pressure sensor was replaced and calibrated once, and the offset is currently at 2 HPA - that's fine?

Here's a summary of all the values:

Offset -2 hPa.
Oil ash 012.
The calculated mass of ruthenium is 6.5 grams.
Russia measured -8.
Regeneration every 280 - 350 km.

I would appreciate it if someone could provide an objective answer, as I am genuinely interested in the matter .

The oil ash is a value calculated by the MSG. It is not a measured value.
If your car's fuel gauge shows only 10% of the maximum level at 176,000 km, that's significantly lower than normal. It's likely that the tuner messed up the DPF data, causing the gauge to display an incorrect reading.

However, if it's emitting visible black smoke from the exhaust, the DPF is likely clogged. I strongly suspect that a G6 model should already have a closed DPF system.

The oil ash shown is not the cause of any error messages. Therefore, there are also models with 65g of oil ash that work perfectly fine, even though the maximum specification is 60g.
It is actually the back pressure, or the maximum differential pressure, that causes this. Therefore, it doesn't help to reduce the amount of oil ash, even if the container is full.

What is your maximum differential pressure during a full-throttle acceleration to maximum RPM? Ideally, in third gear, but preferably in fourth gear.

guste100 wrote:

The oil ash is a value calculated by the MSG. It is not a measured value. If your car's fuel gauge shows only 10% full at 176,000 km, that's significantly lower than normal. It's likely that the tuner messed up the DPF data, causing the gauge to display an incorrect reading. If it's emitting visible black smoke from the exhaust, then the DPF is likely clogged. I strongly suspect that a G6 model should already have a closed DPF system. The oil residue shown is not the cause of any error messages. Therefore, there are also models with 65g of residue that function properly, even though the maximum specified limit is 60g. It is actually the back pressure, or the maximum differential pressure, that causes this. Therefore, it doesn't help to reduce the amount of oil sludge, even if the container is full. What is your maximum differential pressure during a full-load acceleration to maximum RPM? At least in third gear, preferably in fourth gear.

The DPF has a filling level of 120 ml. When it reaches 175 ml, it is full. I find this value to be normal at 176,000 km.

Under load, I think it was around 200 mbar.

The question remains: why is the measured value in the negative range of the ash content, even in cars with a functioning DPF?

janniskre wrote:

The DPF has a loading of 120 ml.

Oh, I misinterpreted your previous "012" as "12ml". My mistake. 120ml should be the correct amount for the mileage. So, please disregard that part of my previous post.

janniskre wrote:

The question remains, why the measured value is in the negative range of the ash, and this is also the case for cars with a functioning DPF

.
You are confusing ash and soot. Are you clear on the difference?

While soot technically cannot become negative, it's just a calculation model. It calculates the maximum possible soot level based on the given ash level (the more ash, the less soot can fit). Then, based on the differential pressure, it calculates how much soot is actually present and displays that value. If the model expects a higher pressure (e.g., because it calculates more ash than is actually present), the calculation result will become negative.

Regards,
Guste.

"Typically, the 'soot levels' I measure are lower than the calculated values. Depending on which limit is reached first, a regeneration process is initiated. And during this regeneration, I observe negative 'measured values'."
hg
Herbert.

"I know the difference between soot and ash; I've just sometimes confused the terms. However, I still don't quite understand the concept of 'negative soot.' I find it strange that even in vehicles with a functioning DPF, the soot measurement sometimes shows a value of -5 grams."

...but Guste and I have now explained it sufficiently.
hg
Herbert.

Please log the exhaust gas temperature before the turbo, and the air-fuel ratio, if possible, both overall and in the exhaust. Then, accelerate fully from 3rd to 4th gear, and if possible, to 5th gear.
Most tuners completely disable the speed limiter via exhaust gas temperature, and the DPF cannot tolerate excessive temperatures, nor might the fuel injection timing maps be properly adjusted.