[T6_measured] DPF regeneration vs. short journeys

[mmi]

Got curious how T6 copes with doing short journeys. And how short would be too short for successful DPF (Diesel Particulate Filter) regeneration.

The graphs below are result of doing short journeys - the plotted one is number 3, thus two interrupted DPF regens before this. At this stage the regen was about halfway through - the DPF regen process was initiated at soot level of approx. 30 grams. The engine is T6 CXEB with recently updated software. Among other things, the DPF regeneration process was altered with the update.

I believe (based on quite a few similar samples) the case here is pretty much "worst case" scenario because outdoor temperature was -1C, city driving (see speed and RPM plots further down).

Picture 1.
Soot level vs. time, including EGR (Exhaust Gas Recirculation) valve position data. The latter just to indicate when the active DPF regeneration takes place.


Picture 2.
The exciting part - the DPF heat-up phase. This is just a subplot of the above - first 480 seconds = 8 minutes.

The conclusion: approx. 7 minutes is needed to get back at same soot level as at engine startup. By doing only shorter journeys the soot level would keep going up, eventually turning DPF warning light on. The exact level for T6 to be defined... assuming to be 35 grams.

Picture 3. Exhaust temperatures along exhaust

Green = engine exhaust manifold, entering turbo.​

Grey = turbo output, entering catalytic converter​

Red = catalytic converter output, entering DPF​

Blue = DPF output​

Data from IDE04090 - Exhaust temperature bank 1. Exhaust details p.27 onwards in https://www.t6forum.com/downloads/the-t6-2-0l-tdi-ssp-564.49/​

Picture 4. Driving conditions during heat up phase.
Outdoor temperature -1C.

Orange = Engine RPM/100 (during heat up average 1350 rpm, decided by DSG).​

Grey = Vehicle speed (during heat up average 34 km/h)​

NOTE: Elevated tick over for first 25 seconds is because of cold weather, not because of pending DPF regen.

Another one in series "[T6_measured]" - ​

[T6_measured] Fickle fuel consumption on MFD – encore

In March 2020 finally got the long-awaited ECU (Engine Control Unit) software update. Unfortunately it took a while to get a good chance to do some measurements to try to figure out what has been changed. So finally a few weeks back dusted the VCDS and collected all kind of intriguing data. The...

www.t6forum.com

​

Comments? Anything else?

 

[mmi]

Reserved. Working on this post... adding more graphs... will bump up the thread when finished...

Picture 5. Exhaust temperatures over "full" DPF regeneration.
Note: here "full" DPF regeneration was from soot level 17.7 grams down to 9.0 grams - as this was the remainder of what was left after two short journeys with unfinished DPF regeneration. Normal case would be from 30.0 grams down to 9.0 grams (for this specific ECU software, there are other high/low limits within T6 EU6 engine family).

GREEN = engine exhaust manifold, entering turbo. GREY = turbo output, entering catalytic converter. ​

RED = catalytic converter output, entering DPF. BLUE = DPF output​

Worth to note that exhaust temperature for the DPF is bumped up and stabilized to 600 C+ in catalytic converter.

These engines do not have extra injector for DPF cleaning, instead during active regen they initiate yet another injection burst outside of power stroke at about 190..210 degrees (after TDC), so injecting fuel into cylinder when exhaust valve is open and piston travelling up pushing the remaining gases and that extra dose of vaporizing fuel out to catalytic converter.





Picture 6. Driving conditions over "full" DPF regeneration.

Orange = Engine RPM/100​

Grey = Vehicle speed​

Statistics over "full" DPF regeneration.

Outdoor temperature -1C.​

Length of the journey 12.3 km.​

Time used 20 minutes.​

Average speed 36 km/h,​

Engine in average doing 1330 RPM as decided by DSG.​

Fuel burned 1.56 litres, which would equal to 12.8 litres/100km = 22.2 mpg.​

On the return journey amount of fuel used was 1.07 litres, which would equal to 8.7 litres/100km = 32.6 mpg. Average speed 35 km/h.​

​

 

[Dellmassive]

Awesome work =)

 

[Robert]

Again Matti, impressive effort and admiring level of professionalism!
Your write-ups are so comprehensive that it is truly hard to add anything.

 

[Deleted member 47066]

Hi all I found this thread while looking for the cause of my very high fuel consumption of my T6 204 (CXEB) with 226kkm in the clock, 20mpgish or 13+ l/100km that is during mostly 100km trips at about 110-120km/h pace. I have it for two months so not much experience but I know how to drive a van and how I consiously I drive should not cause anything higher than 5l/100km, LOL.
It has a recently changed EGR unit following some DTCs indicating its fault and check engine light coming up for most probably leftovers building up in DPF (just days after purchase). Garage said the DPF buildup was caused by the car not being able to regen having the DTC active but after some investigating I think it was most probably for having it run with low fuel levels for few hundred kms. Or maybe both?
Anyways. What I see now 2 full tanks after the EGR change is the very high fuel consumption. No DTC currently.
I have access only to an OBDeleven device and my phone but on my most recent trip I was checking some live data which showed that “service regeneration current duration” data was counting up to around 600s, calculated and measured ash levels going down from 25ish values to 10ish grams. Seems okay but when it finished, started again in a few minutes. Time and distance since last regen was comfirming these frequent regens.
Now, writing this I realize I had a 700km trip BEFORE the EGR replacement as I had to wait for the scheduled repair to come with motorway+country roads about half:half, motorway speeds mostly 130-140kmh not having to refill during the whole trip. Obviously much lower than the current 13+ consumption. EGR replacement was due then already and we were after a forced regen to get the van back to life after the check engine light indicating its DPF neimg clogged. What went wrong around the EGR change then?

Thanks for reading it so far and if you’re still here… I hate how much it consumes and read everywhere it is not normal. I would like to know the root cause but I’m stuck without a knowledgable garage/technician I trust, unfortunately. Am I on the right path to suspect frequent regens causing the high fuel consumption? Should it be something else?
Thank you for any advice in advance.

 

[mmi]

calculated and measured ash levels going down from 25ish values to 10ish grams. Seems okay but when it finished, started again in a few minutes.

Did you happen to make a note of the values when the regen started again?

Am I on the right path to suspect frequent regens causing the high fuel consumption?

Probably - if the engine indeed is more or less in permanent DPF regeneration it definitely will guzzle 12-14 litres/100km. See my post above Statistics over "full" DPF regeneration.

I would start checking condition of the DPF itself:

1) What's reported ash mass -

OBD11 Particulate filter, oil ash mass?​

2) What's differential pressure across the DPF when hot engine (after 15 min drive) is idling at 830 RPM?

OBD11 - Particle filter, differential press. sens 1 bank 1 raw value​

For the above make also notes of​

Air mass, actual value​

Exhaust recirc. valve 1 bank 1, posit feedback - act.value​

Exhaust temperature bank 1 (S3, S4)​

Particulate filter soot mass calculated​

Particulate filter soot mass measured​

​

3) Shut off the engine and turn ignition immediately back on - read again (just to record sensor offset)

OBD11 - Particle filter, differential press. sens 1 bank1 raw value​

4) Please post OBDeleven data from

Control units > Engine > Info​

Control units > Engine > Faults (if any)​

 

[Deleted member 47066]

@mmi thanks for picking this up, appreciated.

New observations are:
- calculated and measured soot mass right after regen finished are around 9 g each
- measured soot mass starts to climb up to 30 g in the following approx 3 minutes and during this time the calculated is down on the approx 9 g level where it ended up after the regen
- when measured soot mass reaches 30 g regen starts again and calculated value jumps up to the same value than the measured one
- the above symptoms have been observed while driving. After reaching destination and letting regen finish engine idle goes down, values stay where they are and even when letting the engine run for like 15 minutes even the measured soot mass level stays where it is (ie does not climb up as it does during driving)

I made notes of the values requested above but not after 15 minutes - as it was during regen once engine warmed up - but when regen finished in about 20 minutes after being triggered, so approx 30-40 minutes after starting up the engine. I'm not so confident that regen was finished though when recording these values below as soot mass values are too high compared to those I usually see. Sorry I'm not a technician and may not be able to get the right data under right circumstances.
- Particulate filter, oil ash mass: 86,81 g
- Particle filter, differential press. sens 1 bank 1 raw value: 105 mbar
- Air mass, actual value: 11,28 g/s
- Exhaust recirc. valve 1 bank 1, posit feedback - act.value: 24,42%
- Exhaust temperature bank 1 (S3, S4): 562,5 C and 474,5 C respectively
- Particulate filter soot mass calculated: 19,06 g
- Particulate filter soot mass measured: 19,03 g

One day and 150km later parking on my driveway having both calculated and measured soot mass sitting on the same level of 11,58 g and engine idling on 830 rpm differential pressure was 62 mbar, exhaust recirc vale on 23,75% and air mass on 10,03 g/s. Exhaust gas temperature sensors way below the "right after regen" values, on 245 and 275 degree Celsius values. Just a few seconds later, after turning off he engine and then ignition back on, particle filter differential pressure down to 1 mbar, air mass zero, exhaust recirc valve at -0,28%.

Hope despite the imperfections the above data is useful and brings us closer to suspecting the root cause of frequent regenerations.

Ah well, Engine info:


No fault codes.

 

[mmi]

Thank you very much - very interesting...

Ah well, Engine info:

Software 04L906056AE version 6206 is up-to-date engine software for class M1 T6 (VIN:WV2...) T6, FWD, DSG.

I made notes of the values requested above but not after 15 minutes - as it was during regen once engine warmed up - but when regen finished in about 20 minutes after being triggered, so approx 30-40 minutes after starting up the engine.

Yes, the 15 minutes was just a kind of minimum to get things warmed up - thus anything more is even better. Also it was necessary to get the readings outside regen.

I'm not so confident that regen was finished though when recording these values below as soot mass values are too high compared to those I usually see. Sorry I'm not a technician and may not be able to get the right data under right circumstances.

Did you drive during the regen - asking because the regen actually just doesn't finish at standstill? The engine can't keep exhaust temperatures high enough long enough when idling (even at elevated idle) - it's no more than 6-8 minutes temps stay high enough. Also the soot levels (19 g) suggest that the engine indeed gave up the regen. Also EGR being at 24% indicates engine not doing regen anymore, the same with exhaust temperatures - still hot but not hot enough - just given up the regen.

- Particulate filter, oil ash mass: 86,81 g
- Particle filter, differential press. sens 1 bank 1 raw value: 105 mbar
- Air mass, actual value: 11,28 g/s
- Exhaust recirc. valve 1 bank 1, posit feedback - act.value: 24,42%
- Exhaust temperature bank 1 (S3, S4): 562,5 C and 474,5 C respectively
- Particulate filter soot mass calculated: 19,06 g
- Particulate filter soot mass measured: 19,03 g

OIl ash mass 86,61g is normal for 230000 km driven. Would reach the maximum 110 g at approx. 300000 km. However, I believe this is just a calculated value - probably based on fuel consumed, driving hours, etc - thus not much value here.

THEN - Particle filter, differential press. sens 1 bank 1 raw value: 105 mbar is extremely high - although because of high DPF temperature (exhaust 562 C/474 C) it's somewhat higher than under "normal" conditions. Anyways see next chapter below...

One day and 150km later parking on my driveway having both calculated and measured soot mass sitting on the same level of 11,58 g and engine idling on 830 rpm differential pressure was 62 mbar, exhaust recirc vale on 23,75% and air mass on 10,03 g/s. Exhaust gas temperature sensors way below the "right after regen" values, on 245 and 275 degree Celsius values. Just a few seconds later, after turning off he engine and then ignition back on, particle filter differential pressure down to 1 mbar, air mass zero, exhaust recirc valve at -0,28%.

I believe here the conditions are perfect - it's been a while since full regen, engine exhaust temperature (actually DPF temp) is at reasonable level.
However, "differential pressure was 62 mbar " is still way too high I believe.

On my engine, also CXEB (but only 75000 km) the differential pressure is below 10 mbar even just before regen (thus full of soot) when EGR at 30-35% (it's vitally important to record also the EGR position as it hugely affects the intake/exhaust flow).

The ignition off, back on, then recheck differential pressure reading was to verify that actual 0 mbar is indeed close to zero on sensor - thus no obvious fault at the sensor (I have observed slack of ±2 mbar by doing the same).

Conclusions based on the above - it's either the differential pressure sensor which is giving too high readings but not detected faulty by sensors self-diagnosis.
OR
the DPF is so clogged that even almost continuos regen doesn't clear it any more.

1. I would start by replacing the DPF pressure difference sensor (part no: 04L906051L --> 04L906051AB) and recheck pressure readings (easy, not expensive). There was a recall to replace the pressure sensor on MY16-MY17...
2. I would check pipework between the pressure sensor and the DPF - as a clogged/split pipe would create pressure on one side of the sensor.
3. The worst case scenario is clogged DPF

---

---

New observations are:
- calculated and measured soot mass right after regen finished are around 9 g each
- measured soot mass starts to climb up to 30 g in the following approx 3 minutes and during this time the calculated is down on the approx 9 g level where it ended up after the regen
- when measured soot mass reaches 30 g regen starts again and calculated value jumps up to the same value than the measured one
- the above symptoms have been observed while driving. After reaching destination and letting regen finish engine idle goes down, values stay where they are and even when letting the engine run for like 15 minutes even the measured soot mass level stays where it is (ie does not climb up as it does during driving)

Very interesting behaviour - thank you for excellent description

Normal behaviour is that "Soot calculated" runs from 9 to 30 grams which then triggers DPF regen. At the same time "Soot measured" runs from -4.5 grams to +2.0 grams (yes, indeed from minus 4.5 grams). "Soot calculated" and DPF regen is as regular as clockwork. In "Soot measured" there is some slack but they go hand in hand from mentioned minimums to maximums.

My guess what's happening - the "Soot measured" is simply based on pressure difference across DPF and used as an emergency trigger for DPF regen because ECU thinks something has gone suddenly wrong as the actual pressure across DPF is way above expected/acceptable value. On another forum it has been vaguely mentioned that when DPF gets clogged it looks like the "Soot measured" takes the controls... however, no actual data was ever posted.

 

[Deleted member 47066]

Thanks for the response and sorry for the slow feedback.

Re driving during regen. Yes I drove during some regens, don't know whether values have been posted from that session or from another. I got lost a bit. What I still know is, during driving regen lowers soot values to 8-9 grams which is fine. I don't know when the 19 grams were captured. The values go up during driving to the 30 grams where the regen starts again DURING DRIVING, not when parked (and engine running of course). 100ish mbars differential pressure was captured after regen on idle. 62 too, don't know why the 2/3 value in the latter case. But as you mention, still too high.

Meanwhile, a friendly technician jumped in and helped me to source the newest numbered part of the pressure sensor as well as to organize cleaning the DPF once done so as to avoid the dirty (even though not to the limit yet) DPF messing up the new sensor or cleaned pipes after the service. Well, I wanted to avoid this DPF renewal but it is worth a try as it is exactly a magnitude cheaper then replacing the DPF.

The worst in the situation I have to wait for almost one month for the service and even though the car's at home I don't use it to avoid injecting liters of diesel into the catalytic converter and then the DPF. Not to mention the high consumption but that alone would not be a big problem. Trying to save whatever can be saved but the car is still parked. Bummer.

 

[Deleted member 47066]

Normal behaviour is that "Soot calculated" runs from 9 to 30 grams which then triggers DPF regen. At the same time "Soot measured" runs from -4.5 grams to +2.0 grams (yes, indeed from minus 4.5 grams). "Soot calculated" and DPF regen is as regular as clockwork. In "Soot measured" there is some slack but they go hand in hand from mentioned minimums to maximums.

Just noticing something strange here. I have a diagnosis log from before I bought the car, like 2000 km before. And I drove another 1000 until the EGR got finally replaced. It had the P046C00 back then already so I knew about that one. I see on the sheet that both calculated and measured soot levels are on 15 g after 31 km driven since the last regen. So the two values go hand in hand (although this is just a snapshot but I believe they do otherwise those being equivalent has close to zero chance), and 'measured' is nowhere around the -4.5...+2.0 grams as you mentioned. Total oil ash mass is not on the log sheet, unfortunately.

Does this lead to any more thoughts about the issue?

Meanwhile, as wrote previously, sensor replacement is scheduled (btw new part number ends 'AB' just introduced in 2021 after the 'L' one) and a few days following that I booked an appointment to clean DPF too. In the days between the two I have time to analyse whether the sensor replacement has solved the issue of frequent regens although if not, I would be hesitant to drive too much so as not to shoot too much shit into the new sensor (piping). Does this make sense?

Would an oil change make sense if it's been 8000 km since the last one and had the EGR issue in the meantime?

 

[mmi]

both calculated and measured soot levels are on 15 g after 31 km driven since the last regen.

So apparently the issue existed already then? 15 grams "soot calculated" would have been "acceptable" if the van was driven just short trips (3-8km).

an appointment to clean DPF

They surely know that on T6 NOx catalytic converter (the NOx trap) is integral part of the DPF - just to treat it properly.

I have time to analyse whether the sensor replacement has solved the issue of frequent regens

I believe it would be seen immediately - just by monitoring DPF differential pressure right after starting the engine. For cold engine/exhaust/DPF the pressure is significantly lower than at operating temperature - on mine the sensor reads well below 10 mbar when cold.

as not to shoot too much shit into the new sensor (piping). Does this make sense?

There shouldn't be any flow in the pipework - unless there is a crack/leak in the pipework.

Would an oil change make sense if it's been 8000 km since the last one and had the EGR issue in the meantime?

Well, surely wouldn't harm because almost continuos DPF regeneration likely has diluted oil with diesel.

---

Below a few mentions about "unexpected" behaviour of "soot measured".

Calculated v actual soot mass - ApplagApp Forum

www.applagapp.com

Jump in Calculated Soot Mass - Page 2 - ApplagApp Forum

www.applagapp.com

Skoda Octavia III 1.5 TDI 2015 Greenline DPF - Weird data please help interpret! - ApplagApp Forum

www.applagapp.com

DPF soot

What’s the difference between soot measured and calculated I have been having my car doing regen it went away and stopped reving a little while ago then come back I drove at 40/50mph air con on 2500 rpm for 15/20 mins a couple of trips before when I scanned it was at 18.00g now it’s down to...

forums.ross-tech.com

Soot mass jumping causing frequent regens.

Hello all, I have a 2015 2.0 Passat GT Estate with just over 92,000 miles. The car runs great but lately its regening every 40 miles. The soot mass drops after regen and it jumped from 6.51g to 23.28g in 1 mile causing it to regen again. I have just bought a Hex-V2 from Gendan...

forums.ross-tech.com

 

[Deleted member 47066]

So apparently the issue existed already then? 15 grams "soot calculated" would have been "acceptable" if the van was driven just short trips (3-8km).

I don't know about their habits and don't trust them as much as to ask. But apparently it was there already, yes. We focused on the EGR issue but these two might have gone hand-in-hand, right?

They surely know that on T6 NOx catalytic converter (the NOx trap) is integral part of the DPF - just to treat it properly.

I hope so. They seem to be knowledgable, provide warranty over their services so yes, I hope. I only want to visit them if the new sensor doesn't solve the issue.

I believe it would be seen immediately - just by monitoring DPF differential pressure right after starting the engine. For cold engine/exhaust/DPF the pressure is significantly lower than at operating temperature - on mine the sensor reads well below 10 mbar when cold.

There shouldn't be any flow in the pipework - unless there is a crack/leak in the pipework.

In which case I'm going to see right after starting the engine and calibrating/learning the new sensor whether it works? I believe idling might be able to show whether the new sensor indeed sends lower pressure values but soot values go up currently only when driving not idling so I think a test drive with live data monitoring would not harm either. Btw, how does the new sensor calibration work? How can we tell the ECU what to do with the sensor? Is calibrating only letting the ECU know that a new sensor has been installed thus asking to forget values received from the old one or should it also been 'told' which voltage levels constitute to particular pressure levels? In the latter case, how on earth to calibrate it properly? In the independent garage we replace it there's no VCDS only some generic tool (Delphi).

Below a few mentions about "unexpected" behaviour of "soot measured".

Calculated v actual soot mass - ApplagApp Forum

www.applagapp.com

Jump in Calculated Soot Mass - Page 2 - ApplagApp Forum

www.applagapp.com

Skoda Octavia III 1.5 TDI 2015 Greenline DPF - Weird data please help interpret! - ApplagApp Forum

www.applagapp.com

DPF soot

What’s the difference between soot measured and calculated I have been having my car doing regen it went away and stopped reving a little while ago then come back I drove at 40/50mph air con on 2500 rpm for 15/20 mins a couple of trips before when I scanned it was at 18.00g now it’s down to...

forums.ross-tech.com

Soot mass jumping causing frequent regens.

Hello all, I have a 2015 2.0 Passat GT Estate with just over 92,000 miles. The car runs great but lately its regening every 40 miles. The soot mass drops after regen and it jumped from 6.51g to 23.28g in 1 mile causing it to regen again. I have just bought a Hex-V2 from Gendan...

forums.ross-tech.com

Very interesting reads and bring me closer to understand how calculated and measured values work/mean, thanks!

Despite this might be the end of this saga with my van I firmly believe that diesel technology and VW cars have gone so complicated that they should be avoided to buy and run if you don't explicitly have to. I don't have to have a van just wanted it to enjoy family trips more. But now we don't enjoy them as the van is stranded. If this one gets resolved we can use it until the next issue pops up. Coming from using Toyota hybrids for the past couple of years it's unacceptable. Why would a regular driver be so knowledgable about the car in order to use it I don't like this. Hope this one (van, LOL) get sorted only to be able to sell the van right after and not looking back. Sad because it is so good to drive and use when it actually works only it doesn't for the majority of times since I have it.

 

[mmi]

Btw, how does the new sensor calibration work? How can we tell the ECU what to do with the sensor?

I believe there is no calibration for the sensor - just plug it in.

a) Engine repair manual doesn't mention calibration.​

b) Engine repair manual doesn't even mention any need to connect "Vehicle diagnostic tester" for renewal of this sensor.​

c) There is no procedure related to this sensor in VCDS or OBDeleven neither in "Basic Settings" nor in "Adaptations"​

 

[DXX]

If sensor calibration was possible it would open up the possibility of false offsets to create false readings. Probably something VW are wanting to avoid at all costs.

 

[Deleted member 47066]

I believe there is no calibration for the sensor - just plug it in.

a) Engine repair manual doesn't mention calibration.​

b) Engine repair manual doesn't even mention any need to connect "Vehicle diagnostic tester" for renewal of this sensor.​

c) There is no procedure related to this sensor in VCDS or OBDeleven neither in "Basic Settings" nor in "Adaptations"​

Thanks, appreciated. Looking forward to see if the new sensor solves the issues.