FYI: DPF regen info from my '09 TDI

I've just stumbled across the DPF regeneration info in the newest version of VAG-COM. It's under 'Drivetrain'. FYI, here's what my car is showing:

Group 108:
Particle filter carbon mass (spec.): 14.4 (grams, I'm guessing)
Particle filter carbon mass (act.): 0

Group 105:
Requested regens: 3
Distance driven since last regen: 220 km
(note: I currently have 6029 miles on the clock, so subtracting from this 220 km (= 137 mi.) means I've had 3 regens in 5,892 miles, or real close to one regen every 2,000 miles, on average. Your mileage most certainly may vary...I'm a 'no-smoke' kinda driver.) Disclaimer: in my most recent post (#20, on p. 2) I retract this conclusion. Further observation has indicated that the "Requested regens" parameter is not a counter for the number of regens. Truth to tell, I have not a clue what it is. In the immortal words of Rosanne Rosanadana: "Never mind!"

Now that I know where this info is, I'm going to try to catch the next regen event 'in the act' in order to collect some interesting VAG-COM data on it.

Thanks for the useful info, `Dawg. :thumbup: I've stickied this thread for the benefit of other `09 owners.

In the immortal words of Goofy: "Gorsh! (Hee-uck!)"

I'm STICKY!

Keep an eye out if the radiator fans come on during the event.

What VAG-COM data would y'all like to see me collect during my next regen?

DoctorDawg said:

I've just stumbled across the DPF regeneration info in the newest version of VAG-COM. It's under 'Drivetrain'. FYI, here's what my car is showing:

Group 108:
Particle filter carbon mass (spec.): 14.4 (grams, I'm guessing)
Particle filter carbon mass (act.): 0

Group 105:
Requested regens: 3
Distance driven since last regen: 220 km
(note: I currently have 6029 miles on the clock, so subtracting from this 220 km (= 137 mi.) means I've had 3 regens in 5,892 miles, or real close to one regen every 2,000 miles, on average. Your mileage most certainly may vary...I'm a 'no-smoke' kinda driver.)

Now that I know where this info is, I'm going to try to catch the next regen event 'in the act' in order to collect some interesting VAG-COM data on it.

Click to expand...

If this info is readily available to you, it would be nice to see if the carbon mass (act.) increases between now and the next regen event. Just wondering if that's what the trigger is.

Doctor, I was wondering if you do a lot of highway driving and if that's the reason why you have had so few regens for 5800 miles. If the 09 TDIs regen so seldomly it shoudn't have much of a negitive impact on mpg. I drive my 09 tdi about 90 % highway I've yet to hear my radiator fan turn on.


09 JettaTDI DSG 4200 miles
06 Jetta TDI DSG 68k sold

Otto Von Diesel said:

Doctor, I was wondering if you do a lot of highway driving and if that's the reason why you have had so few regens for 5800 miles. If the 09 TDIs regen so seldomly it shoudn't have much of a negitive impact on mpg.

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Yep, as you can see from the fine print in my sig, I do mostly highway (70%) and country (15%) driving...which has a lot to do with why I see such good fuel economy. And I absolutely agree with you, Otto; at one regen per 2K miles, the effect on fuel economy must be really quite minor. That's one of the pieces of data I'd like to try to collect during the next regen: fuel injection quantity. From that, plus the frequency of regens, one can make some definitive quantitative statements about the impact of the DPF on fuel economy (which I'm willing to bet will be a very small impact).

I'd be interested in knowing what your water temps are when a regen cycle occurs. I do mixed, edge of city driving, and my water temp gets up to 200 a lot (assuming SG is accurate) and I hear the fans going. I don't know if I regenerate frequently, or if can runs higher temps than previous diesels, or if I have a problem of some sort.

More secrets of the '09 DPF

I've been making some further observations of the DPF via VAG-COM since the OP, and have learned a few things:

1. Somewhat counterintuitively, the value for "Particle filter carbon mass (act.)" never changes; it stays at zero, day-in and day-out. I'm guessing this would be the value determined by an actual carbon sensor if the DPF had one, which it apparently does not.

2. On the other hand, the value for "Particle filter carbon mass (spec.)" does change, on the order of once every 5 minutes or so, while you drive. It can go up, or it can go down. As I mentioned in my OP, when I first discovered this parameter its value was 14.4. This morning, when the missus and I went out for brunch, its value was 12.0 prior to starting the engine (still only 3 regens shown by VAG-COM, so its decrease was not caused by a regen), and over the course of a 20 minute mostly-city drive it increased, in three steps, to 12.9. I recall reading sommers that ECU determines when a regen is needed based on two things: (i) the pressure differential across the DPF, and (ii) the results of a model of carbon accumulation based on your driving profile. So I'm guessing that "Particle filter carbon mass (spec.)" stores the predicted carbon accumulation calculated by this model.

3. OK, this one's really interesting. When you log the pre-DPF and post-DPF temperatures while driving, when the engine is under load (accelerating or climbing a hill) you'll observe that the pre-DPF temperature is higher than the post-DPF temperature...no big surprise here. BUT...when the engine is not under load (while coasting, driving on the flat with no acceleration, or idling) the pre-DPF temperature drops more than the post-DPF temperature does, so that the post- temperature actually ends up (and stays) higher than the pre- temperature. The graph below documents this (data is from a fully warmed-up engine that had been idling for about 3 minutes before data collection started):



(Between 140 and 180 seconds on this graph I brought the RPMs up to 2000 (while still in Park), because I want to use the pressure differential at 2K RPM in Park as my standard measure of DPF obstruction in future).

Notice how the post-DPF temperature stays 12-15 *C higher than the pre- temperature (except while I'm revving the engine)? There are only a few things that could account for this:

(a) The DPF has an electric heater. Not a chance. Fuggedabadit!

(b) Condensation of vapor to liquid within the DPF is heating it. This is formally possible, but I don't believe it. How much condensation would you be seeing at around 200 *C? And if you were seeing enough to heat the DPF by 12-15 degrees, you'd have liquid pouring out of your tailpipe.

(c) By far the most plausible explanation is that the DPF experiences some measure of passive regeneration during normal operation...i.e., some soot is oxidizing continuously inside the DPF, which would indeed heat it somewhat. In my recent readings regarding DPFs I've seen it mentioned several times that passive regeneration can indeed occur, but it is more or less efficient in different exhaust system designs. It is most efficient when the NOx trap or cat is placed after the DPF, because NOx is a strong oxidant and so will promote some oxidation of soot in the DPF at normal operating temperature. If I'm reading correctly the picture of the exhaust system recently posted by Drivbiwire, that appears to be the case in the '09: the NOx storage catalyst is downstream of the DPF(?).

So I'm thinkin' this is a good thing! The more passive regeneration the DPF does, the less active regeneration it needs...and, thus, the less of a hit it imposes on fuel economy, since active regen requires extra fuel supplied via post-combustion injection, whereas passive regen is essentially free. Yay, VW!

Something else which this observation suggests is that the more you drive in such a way as to stay out of the smoke zone, the less soot you deposit in the DPF, and thus the better its chances of keeping itself unobstructed via passive regeneration rather than requiring an active regen...and, thus, the better your MPGs. So there's yet another way in which smoke kills your fuel economy, folks.

Last night, I went out to the car and check it with VCDS and saw that the Requested Regens was at 4. I did a 200 mile trip today and checked the car again and found that Requested Regens was now at 3. The car had approx 1500 miles on it at the beginning of the trip and 1700 when I got home. It seems that the regens are not by mileage accumulated, but by a time period that the system feels it needs a regen.

El Dobro said:

Last night, I went out to the car and check it with VCDS and saw that the Requested Regens was at 4. I did a 200 mile trip today and checked the car again and found that Requested Regens was now at 3.

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Now that is purely puzzlin'. I'll be monitoring mine weekly. I'd welcome it if you could do the same. Let's figger out what's goin on here....

italian tune-ups....

wonder if you do a italian tune-up periodically, if that would lessen the need for active regens?

For the amount of time that the regeneration process lasts, the extra fuel used will be quite small. Joe

CentralFloridaTDIguy said:

wonder if you do a italian tune-up periodically, if that would lessen the need for active regens?

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Just my opinion, but yes, I expect it would; passive regeneration should happen faster at higher EGTs. However, that's not the same as saying that periodic Italian tune-ups will save you fuel by reducing the frequency of active regens; if your high-rev driving uses more fuel than the avoided regens would have, it doesn't add up.

Took the car to work today, about 35 miles round trip, with a mix of highway speeds, local roads and stop and go traffic. I checked when I got home and the data for the regens from the 200 mile ride were still listed.

Thanks, E.D. I think its going to require a series of regular observations to figger this out. I'm going to be checking mine twice weekly until my next regen occurs, then will report what I learn.

Dumb question-what's a regen?

eft said:

Dumb question-what's a regen?

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Not dumb at all. A 'regen' is when the Diesel Particulate Filter (DPF) on the '09 TDI is regenerated by burning all the trapped soot out of it. This is accomplished by the computer by ordering a series of post-combustion injections of fuel into the cylinders; this unburned fuel travels down the exhaust system, hits the hot DPF, and burns, raising the DPF's temperature high enough (about 600 *C, IIRC) to burn soot. Regens are triggered by the computer in response to one of two things: either the pressure differential across the DPF gets too high (i.e., the DPF is getting clogged, and restricting flow) or the computer's internal profile of your driving pattern suggests to it that its time for a regen. Presumably the latter works even if the former doesn't; I assume that this is a 'fail-safe' mechanism so that even if the pressure differential sensor on the DPF fails, you'll still get regens at reasonable intervals.

Hmmm....

OK, I can now confirm what El Dobro reported in an earlier post: the Group 108 measuring block value for "Requested regens" on my car has mysteriously declined from its value of 3 when I first found it on Nov. 2, to a value of 2 today. So, alas, the only thing we know for sure about this parameter is that we don't know anything for sure about this parameter; it is clearly not a regen counter nor even a regen 'request' counter. Sigh. Hence, my estimate of 2K miles between regens is incorrect. With heavy heart, I suggest to the moderator that perhaps this thread should be de-stickied.

Did you use the button to ask them to unsticky it? Keep on with the data gathering. Maybe some kind of a pattern will evolve.

After checking 3 days in a row, the regen figure went from 3 to 4 today, BUT the data didn't change. It still has the figures from the 200 mile ride. I'm wondering if it's also counting regens of the NOx storage catalyst.

El Dobro said:

I'm wondering if it's also counting regens of the NOx storage catalyst.

Click to expand...

But that wouldn't explain why the number goes down sometimes.

Only possibility I can imagine at present: maybe this parameter counts the number of times the ECU requests a regen before it actually gets a regen (regens can't be performed below 40 MPH and 2K RPM). In which case it should get reset to zero after every successful regen. Just pullin this outta my anal orifice here....

I'm interested in using biodiesel in the 2009 tdi. From what I've read on several posts in the forum, understanding the regen process is key to doing this safely. Any chance that the requested regens is a level of regeneration (eg. active vs passive or duration of active) rather than a number of regens performed or requested? A variable level of regen could be influenced by driving pattern and modeled buildup as suggested in vag-com data. This would explain a change in requested regens associated with a prolonged driving pattern that varied from most recent prior patterns. Just a thought.

Its as good an idea as any other at this point, BosR. I'll keep collecting data and trying to figger this out. Stay tuned.

Caught a regen in the act!

I have been monitoring daily several DPF-related parameters, just waiting for a regen to occur on my watch. It happened today. On my commute into work as I exited the freeway onto surface roads my radiator fan came on and my idle speed increased to 900 RPM, but there was no change in performance. Anyway, tonight upon getting home I checked VAG-COM'd the DPF parameters as always, and find that, indeed, a regen did occur.

Here's the data:


The vertical dashed lines represent the mileage at which my last two regens occurred. These are determined by keeping an eye on Engine group 105 "Distance driven since last regen" which, indeed, records the distance driven since the last regen. This value increases steadily as you drive, until you have another regen, whereupon it resets to zero. As you can see, the interval between my last two regens was about 325 miles (rather embarassingly different from the 2,000 mile guess I started this thread with ). The other two items I record daily are:

• Group 108 Particle filter carbon mass (spec.) (which I still believe is based on a model, not on sensor output), and
• A derived value, DPF pressure differential at 2K RPM (lets call it 'Delta-P'), which I calculate by revving the thoroughly warmed up engine to 2K RPM in park while recording the DPF pressure differential (I forget which group this is; its just below 108 sommers).

As you can see, my most recent regen reset the carbon mass to a nice low value, but had absolutely no effect on Delta-P (which had decreased all by itself the day before, on a nice high-speed all-highway drive). Apparently the ECU pays more attention to the carbon mass calculated value than it does to the Delta-P when it comes to deciding when to order a regen.

I'm going to keep recording all this data on a daily basis for a while, and once I have three or four regens' worth I'll repost this expanded graph again here in this thread.

Awesome thread! The folks on this forum will understand before the dealer techs!

It'll be nice if all of this will be covered in the Bentley.

I think part of the reason I bought my new 09 TDI is so that I could get an education here on stuff like this.

Thanks Dr.!

I have read tons about the regen on this forum, but I had a physics test today and all those forumlas have eroded my memory.

Is the post injection JUST for raising the temperatures to burn off soot, or does it regenerate the Nox catalyst, or both, or one of the other things the exaust system does in this car.

Also, how much fuel did the regen use, if you measured fuel usage during the timeframe it took place.