# DPF behavior I have observed.



## firehawk618 (Feb 24, 2013)

I found this interesting. With the Scangauge and Xgauge for "DPF Soot load %" setup and displayed at all times so far for the last 5 days I have noticed my soot load started at 49%. With highway driving and gradual acceleration off the line when taking off I have only seen it go up to 51% and that took 2 days.

Doing some full throttle runs from a stop deliberately trying to add soot I noticed it wasn't too difficult to make that load climb. I had it as high as 57% at one point.

I am doing all this to learn the behavior of the system. Here's where it gets odd to me.

I had the load to around 57% and quit fooling around with it. I figured the quick climb in load was due to me inducing soot into the system by my driving which I expected.

When on the freeway I mashed the pedal when I was already going 70mph. Held it down to get to 90 so basically ran it to the redline.

When I was done and coasted back down I noticed the soot load had gone down to 51%!

ROFL I never imagined the ol' Italian tune up would actually blow soot out of the DPF.

After the trip I am back home and it's at 50% again.

I have almost 700 miles since my last regen and am watching regen status with the Scangauge. So far since I installed the gauge I have not had a regen.

I verified DPF soot load with my Solus and GDS2 and it appears accurate.


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## firehawk618 (Feb 24, 2013)

I want to do a forced regen to see what the soot load sits at after a fresh cleaning yet part of me wants to ride it out and let the car do a regen when it sees fit and at what percentage of soot load it takes to initiate a regen.

My car has around 2400 miles. It's had 2 regens logged and they averaged 8xx miles between regens according to the PCM.

If the 8xx mile thing continues then it's due for another regen soon however if it uses soot load as one of the parameters when deciding when to do a regen then I doubt I'll see one anytime soon.


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## firehawk618 (Feb 24, 2013)

This shot was several days ago. Notice the *DIS* is 238. That's distance since regen. It's around 7xx now and the soot load is lower than displayed in the image.


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## Diesel4Ever (May 30, 2018)

firehawk618 said:


> This shot was several days ago. Notice the *DIS* is 238. That's distance since regen. It's around 7xx now and the soot load is lower than displayed in the image.


It’s doing a passive regen while you’re driven on the freeway. There is enough heat in the exhaust to burn some soot while at speed.

The 800 mile interval may be triggered as a default value, regardless of the % status of actual soot load.


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## firehawk618 (Feb 24, 2013)

From what I understand so far a passive regen doesn't inject diesel in the exhaust stroke and an active one does.

800 is a rough number. It's just the average mileage between my 2 regens that are logged in the PCM. I am doubting there's a hard number it uses to do an active regen whether it needs it or not but would like to see information supporting either argument.


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## firehawk618 (Feb 24, 2013)

I'll wait for my soot load to increase to around 60 if it ever gets that high and do another Italian tune up on the freeway to see if it behaves the same way again.


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## LiveTrash (May 24, 2015)

Even though your gauge may be accurate, keep in mind the sensor is an estimate, not an exact value. Small increments should be taken lightly. However, as mentioned, the decrease in soot is due to the heat buildup from the highway driving. I have never observed this in my Gen 1, but it does it all the time in my work truck. I can only imagine the system in the Gen 2 Cruze is more efficient with the regenerations.


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## Diesel4Ever (May 30, 2018)

firehawk618 said:


> From what I understand so far a passive regen doesn't inject diesel in the exhaust stroke and an active one does.
> 
> 800 is a rough number. It's just the average mileage between my 2 regens that are logged in the PCM. I am doubting there's a hard number it uses to do an active regen whether it needs it or not but would like to see information supporting either argument.


It measures soot load by delta P across the filter.

Some diesels with DPF have a default mileage trigger for regeneration. My TDI does, about every 500 miles. I think it’s a common strategy for keeping the filter clean.


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## firehawk618 (Feb 24, 2013)

Diesel4Ever said:


> It measures soot load by delta P across the filter.
> 
> Some diesels with DPF have a default mileage trigger for regeneration. My TDI does, about every 500 miles. I think it’s a common strategy for keeping the filter clean.


Yes. I haven't looked yet but I would imagine there's a DPF pressure sensor at each end of the filter.

I will keep an eye on things and see over time what the logic GM is using on the system.


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## firehawk618 (Feb 24, 2013)

On a related note. I have to imagine that the auto stop / start is **** on the DPF and EGR of the diesels.

The transit agency I work at has a specific fleet that does have the auto start / stop + cummins ISB and they're nothing but after treatment + egr headaches.


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## firehawk618 (Feb 24, 2013)

I'm at a 800 miles and no active regen. Calculated soot load still sits around 50%. Will climb to 54% and dip to 49% but 50% seems to be it's target.

I'm going to force a regen this evening to see what calculated load it will end up at when done for my information.


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## firehawk618 (Feb 24, 2013)

Well I was sitting at 50% soot load for as long as I have been monitoring it. Curiosity got the best of me so I forced a regen.

To my surprise it seem to zero calculated soot load after the regen.

Pics when I get home


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## froyofanatic (Jul 16, 2018)

Can I see soot load with a OBD2 sensor and an app like Torque?


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## firehawk618 (Feb 24, 2013)

froyofanatic said:


> Can I see soot load with a OBD2 sensor and an app like Torque?



Maybe if you can find and program the PIDs into torque.

I don't use Torque. I want my phone screen clear for other apps, my obdii port is occupied with the Scangauge and I don't want another device on my dashboard.


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## Cruz15 (Mar 17, 2016)

My reader says 0 regens so far, I am at 3100 kms so I doubt its accurate. I have seen the car throw extra fuel in the engine alot more often than the 2015 I had.
So far I am getting worse mileage than my 2015. The engine just cant seem dip down into the 2 - 3 l/100 km like my 2015 did.


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## firehawk618 (Feb 24, 2013)

Cruz15 said:


> My reader says 0 regens so far, I am at 3100 kms so I doubt its accurate. I have seen the car throw extra fuel in the engine alot more often than the 2015 I had.
> So far I am getting worse mileage than my 2015. The engine just cant seem dip down into the 2 - 3 l/100 km like my 2015 did.



What reader are you using?

I have used GDS2 and a high end Snap on tool that is updated to current levels to read mine.

The Scangauge also reads the same as both the tools above.


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## Diesel4Ever (May 30, 2018)

Regen Pro-Tips:

If it's cold outside and you’re in the middle of a Regen and about to shut off the car, don't do it. As the exhaust cools down over night the water vapor inside the exhaust will condense in the soot left in the DPF and form a wet "muck" sludge that will take much longer to finally burn off when you re-start the car. It's best to do the following before the car is parked.

If you notice that you’re in the middle of a Regen, and you plan on parking soon. Or just want to get if over with quick:

Put it in a higher gear 4-6 if a MT, 6-9 in manual mode if the AT, depending on speed limit. Accelerate hard (50-75%+ throttle) up to 4K and then engine brake down to 2k. Repeat. Make sure your coasting down under load after accelerating. Do this 4-5 times and your regen will be done. With all this extra heat and pressure being placed on the DPF it takes like 5 min or less to be completed. A hypermiler told me about it and it works.


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## Barry Allen (Apr 18, 2018)

So, some questions:

Exactly what do these cars do during a forced regeneration? If it's done while parked, why can't this be done by users instead of having to take it to a dealership and have their plug-in computer trigger it?


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## IndyDiesel (May 24, 2015)

Diesel4Ever said:


> Regen Pro-Tips:
> 
> If it's cold outside and you’re in the middle of a Regen and about to shut off the car, don't do it. As the exhaust cools down over night the water vapor inside the exhaust will condense in the soot left in the DPF and form a wet "muck" sludge that will take much longer to finally burn off when you re-start the car. It's best to do the following before the car is parked.
> 
> ...


What you are suggesting does work, I have done it once or twice, but perhaps if it’s an option just keep driving for a few more minutes which is less stress on the car for sure.


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## Rivergoer (Mar 30, 2017)

Barry Allen said:


> So, some questions:
> 
> Exactly what do these cars do during a forced regeneration? If it's done while parked, why can't this be done by users instead of having to take it to a dealership and have their plug-in computer trigger it?


After several failed/incomplete regen attempts, a code sets, car goes to limp mode and cannot be cleared until the dealer plugs in and forces a regen. Something to do with the GM proprietary software...maybe @Robby can expound further. 

Whether users with @Snipesy ‘s Android app can manually command a forced regen under those circumstances, I’m not sure.


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## Robby (Mar 1, 2013)

A 'forced regeneration' is a 'deep cleaning' process that essentially cleans all the treatment systems in preparation for further diagnostics if a problem is present.....or, for this discussion, failure to allow a regen to be completed.
It is more advanced than a normal regen, utilizing a very elevated engine speed, a lot of fuel and a lot of def. It must be performed over a surface that won't combust since the exaust temperature is also elevated and could start a fire.

Related codes generally cannot be cleared (stays in dark memory) unless two successful regens have taken place.

Rob


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## Barry Allen (Apr 18, 2018)

Robby said:


> a lot of def


Why does a regen cycle use a lot of DEF?


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## Taxman (Aug 10, 2017)

I'm guessing it's because it "essentially cleans all the treatment systems".

I didn't think about the exhaust heat. Is it capable of damaging asphalt or tarmacadam?
I imagine most people wouldn't be happy if they made a rough molten depression in their driveway while running a manual regen. (or if they warped the back bumper)


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## Robby (Mar 1, 2013)

Taxman said:


> I'm guessing it's because it "essentially cleans all the treatment systems".
> 
> I didn't think about the exhaust heat. Is it capable of damaging asphalt or tarmacadam?
> I imagine most people wouldn't be happy if they made a rough molten depression in their driveway while running a manual regen. (or if they warped the back bumper)


Although a lot of radiant heat is given off, fortunatly, heat rises......I have never (yet) seen asphalt damage but I've only been over concrete when forcing a regen.

To Barry Allen: Def creates a reaction in the catalyst to help clean it. During a forced regen the engine runs at a fairly high speed to get the exaust hot and then injects a rather rich def mixture. During the regen the So2 sensor(s) response is monitered through the ecm....it is looking for a rather abrupt signal ahead of the cat and a stable signal post cat.....this is how the ecm knows the cat efficiency is restored.

The car should never require a forced regen if it has been allowed to complete normal regeneration cycles and no treatment systems have failed.

Rob


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## Taxman (Aug 10, 2017)

Robby said:


> The car should never require a forced regen if it has been allowed to complete normal regeneration cycles and no treatment systems have failed.


I thought the 2014-2015 *DPF* (edit: how did that come out as DEF when I posted this?) system was programmed to fail if you shut the engine off just before regeneration started. Does anybody know if they cured that in the 2017-2019 models? 

One of our members suffered a 'pay us to do a forced regen under warranty' failure in a nearly new 2018 this month, but I'm not sure if it's from turning the car off at the wrong time, or from replacing the headlights as the dealer claims.


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## Barry Allen (Apr 18, 2018)

Robby said:


> Def creates a reaction in the catalyst to help clean it.


I was unaware that DEF does anything to "clean" the SCR catalyst. DEF decomposes into water (which evaporates) and ammonia, and it's the ammonia that reacts with NOx to reduce it to nitrogen, water, and carbon dioxide.


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## Robby (Mar 1, 2013)

Barry Allen said:


> I was unaware that DEF does anything to "clean" the SCR catalyst. DEF decomposes into water (which evaporates) and ammonia, and it's the ammonia that reacts with NOx to reduce it to nitrogen, water, and carbon dioxide.


As presented to me, oxidizing def creates a reaction within the converter that 'burns off' accumulated soot to restore efficiency. There is more to def than water and ammonia......def is actually urea.....man made cow pee-pee.

Rob


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## Barry Allen (Apr 18, 2018)

Robby said:


> As presented to me, oxidizing def creates a reaction within the converter that 'burns off' accumulated soot to restore efficiency. There is more to def than water and ammonia......def is actually urea.....man made cow pee-pee.


DEF is 32.5% urea and 67.5% deionized water. That ratio is standard because the freeze point is the lowest (12°F).

I could be wrong but I don't think DEF has anything to do with "cleaning" the catalyst. The exhaust system in most modern diesel engines is three separate components in the following order:
1. A two-way catalytic converter that cleans up carbon monoxide (not much produced by diesel engines to begin with) and unburned hydrocarbons. CO is oxidized to CO2. Hydrocarbons are combusted to CO2 and water.
2. A DPF filter then catches as much soot as possible, approaching 100% in some situations.
3. Finally, a NOx catalyst uses injected urea to convert NOx into nitrogen, water, and CO2.

During regeneration, the extra fuel injected into the exhaust stream hits the catalytic converter and is combusted in the exhaust stream. This raises the temperature and the DPF then burns off the captured soot, converting that into CO2 and water.

The exhaust coming after the DPF is as clean as it's ever been. The days of seeing diesel engines belching black smoke under load are long gone. I don't think DEF has anything to do with "cleaning" the NOx catalyst so I just can't figure out why it would be consumed in large quantities during a forced regen.

The only reason DEF would be consumed is regeneration while driving to reduce NOx emissions. But a forced regen is parked and there is essentially no regulation of vehicle emissions when they aren't driven on public roads. I could be mistaken again but I can't believe the EPA does any sort of emission testing for parked (idling) vehicles, or diesel vehicles undergoing forced DPF regeneration.


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## Robby (Mar 1, 2013)

Well, speculation to a degree on my part as far as cleaning the SCR (selective catalyst) but because of the heat involved I'm confident it is burning (intentionally) soot from the reactive components to bring it back to good health.
The DEF is injected at a rate of 2% to 6% of diesel fuel consumption measured by volume and, since a lot of fuel is used in a 'forced regen' it stands to reason that def usage will increase accordingly.
The function of the def in the SCR is primarily to assist in NOx reduction.....and I am quoting Wikipedia on this one.

But the original question, def usage during a forced regen, using the percentages above, naturally will increase during the proceedure.

Rob


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## Barry Allen (Apr 18, 2018)

Robby said:


> Well, speculation to a degree on my part as far as cleaning the SCR (selective catalyst) but because of the heat involved I'm confident it is burning (intentionally) soot from the reactive components to bring it back to good health.


Heat from the extra fuel injected and then combusted in the catalytic converter cleans the DPF of soot (by combusting it). DEF is 67.5% water so adding that to the exhaust stream functions to cool the exhaust when the water uses some of the heat to flash into steam. DEF does nothing to raise the temperature of the exhaust; it lowers the temperature of the exhaust.


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## IndyDiesel (May 24, 2015)

When I had a forced regen at dealer when they did the recall and a replacement of a sensor, the car was sitting outside and the regen had the engine running at 3000 rpm and hooked up to a laptop inside the car. It runs for quite sometime to complete the forced regen. Seems weird to hear the engine run that fast in park.


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## Robby (Mar 1, 2013)

IndyDiesel said:


> When I had a forced regen at dealer when they did the recall and a replacement of a sensor, the car was sitting outside and the regen had the engine running at 3000 rpm and hooked up to a laptop inside the car. It runs for quite sometime to complete the forced regen. Seems weird to hear the engine run that fast in park.


Try it on a Duramax.....fan stays engaged and it sounds like it is at 5000rpm.....Sounds like hard parts will be leaving soon.

Rob


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## Robby (Mar 1, 2013)

Barry Allen said:


> Heat from the extra fuel injected and then combusted in the catalytic converter cleans the DPF of soot (by combusting it). DEF is 67.5% water so adding that to the exhaust stream functions to cool the exhaust when the water uses some of the heat to flash into steam. DEF does nothing to raise the temperature of the exhaust; it lowers the temperature of the exhaust.


Sounds reasonable....steam cleaning the system.

Rob


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## boraz (Aug 29, 2013)

injected fuel cleans the dpf

injected def cleans the exhaust within the scr


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## boraz (Aug 29, 2013)

@Robby should really edit your posts

would be very misleading to a new/learning owner


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## Diesel4Ever (May 30, 2018)

IndyDiesel said:


> Diesel4Ever said:
> 
> 
> > Regen Pro-Tips:
> ...


I don’t think accelerating at 50-75% load up to 4K rpm places undue stress on any car as long as the oil and operating temps are normal.

Regen cycles on diesels cause stress, on the engine and emission componenents. Multiple interruptions of said cycle, can also cause issues, eventually forcing a dealer visit.

With that said, getting the regen done ASAP and before shutdown takes place makes a lot of sense...


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## IndyDiesel (May 24, 2015)

Diesel4Ever said:


> I don’t think accelerating at 50-75% load up to 4K rpm places undue stress on any car as long as the oil and operating temps are normal.
> 
> Regen cycles on diesels cause stress, on the engine and emission componenents. Multiple interruptions of said cycle, can also cause issues, eventually forcing a dealer visit.
> 
> With that said, getting the regen done ASAP and before shutdown takes place makes a lot of sense...


Respectfully disagree with you, I would much rather drive my car for maybe 5 min at normal driving vs 4000 rpm without a load on it.


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## boraz (Aug 29, 2013)

IndyDiesel said:


> 4000 rpm without a load on it.


who suggested this?


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## Diesel4Ever (May 30, 2018)

IndyDiesel said:


> Respectfully disagree with you, I would much rather drive my car for maybe 5 min at normal driving vs 4000 rpm without a load on it.


An unassisted DPF regen takes 15-20 minutes with normal driving. The “assisted” regen can be completed in 5 min or less.

I never said to rev to 4K without any load. You need a load on the engine to generate heat, which is also why you’re supposed to use the higher gears.

You need to re-read the procedure as it appears you do not understand what I wrote.


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## IndyDiesel (May 24, 2015)

Diesel4Ever said:


> An unassisted DPF regen takes 15-20 minutes with normal driving. The “assisted” regen can be completed in 5 min or less.
> 
> I never said to rev to 4K without any load. You need a load on the engine to generate heat, which is also why you’re supposed to use the higher gears.
> 
> You need to re-read the procedure as it appears you do not understand what I wrote.


You are correct, my bad. I have done what you are suggesting one time, it’s not a big deal though to just turn car off during regen as long as it is underway, that has happened to me a lot and have had zero issues. I have also had times where I am close to the end of the regen and I just keep driving for a couple more minutes to complete. Everyone has an opinion on it, no big deal.


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## firehawk618 (Feb 24, 2013)

Rivergoer said:


> After several failed/incomplete regen attempts, a code sets, car goes to limp mode and cannot be cleared until the dealer plugs in and forces a regen. Something to do with the GM proprietary software...maybe @*Robby* can expound further.
> 
> Whether users with @*Snipesy* ‘s Android app can manually command a forced regen under those circumstances, I’m not sure.



Is this a known fact with 2nd gens or are you referring to 1st gens?


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## firehawk618 (Feb 24, 2013)

DEF is injected POST DPF and POST SCR. DEF is the last part of the after treatment system.

It does nothing but reduce NOx levels. That's it. 

I am stating these facts based off working regularly on aftertreatment systems on Cummins ISL and ISB engines in transit coaches.

I can sit and watch on a laptop the pre and post SCR NOx levels actively and spot a failing or blocked doser valve without turning a single wrench. With enough experience you kind of know what pre and post NOx you should expect to see on a given engine with a functioning system.

The other after treatment systems I have glanced at also inject the DEF for SCR after all other aftertreatment is done. Every system that I have personally looked at the DEF is last.

I am not saying this is always the case but in my experience it has always been the case.


I encourage people to study their aftertreatment systems the next time you're changing oil on your car. Pull off the underbody aero shield.

You'll see 3 exhaust temp sensors, 2 NOx sensors, 1 doser valve.

First exhaust temp sensor is pre DPF. Second is post DPF and third is post SCR.

The first two are so the ECM can monitor the DPF efficiency during a regen. The second and third are to monitor SCR efficiency.

If you want to know exactly where the DPF and SCR are on your car use the 3 temp sensors to find them. They basically indicate where one starts and ends.

DEF is injected pre SCR to initiate the reaction in the SCR chamber.

The amount of mis conception and information about aftertreatment systems on modern diesels is overwhelming. *Not on this forum but on the internet in general.*

I had one guy tell me recently that DEF is to raise exhaust temps to cook off soot in the DPF. *FACEPALM*


EDIT: Edited to correct a few things.


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## firehawk618 (Feb 24, 2013)

Also if you have a scan gauge and want to watch your exhaust temps during a regen monitor the 2nd one. The one post DPF. That one will skyrocket to 1100-1200 degrees fahrenheit during a regen. 

If your ECU doesn't see a pretty substantial temperature differential between temp sensor 1 and 2 it will throw a DPF related code because the ECM will know it's either gone *it can also tell by the pressure differential sensor* because the temp won't be much different between temp sensor 1 and 2 during a regen.


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## Rivergoer (Mar 30, 2017)

firehawk618 said:


> Is this a known fact with 2nd gens or are you referring to 1st gens?


Good point. 

I’m no mechanic or GM engineer so I cannot state it’s a “known fact” the Gen 1 and Gen 2 DPF/DIC warnings work the same.

That said, they do appear to behave the same way according to the owner’s manuals. 

Specifically in the 2017 owners manual, pages 143 and 223, the references to DPF “self-cleaning function” are the same. The DPF clean process must complete successfully or a DIC warning is triggered, just like the Gen 1. 

Furthermore the manual states continued driving without completion of DPF self-clean can lead to Reduced Engine Power warning.

Whether or not this situation (on a Gen 2) can eventually lead to a trip to the dealer for a forced Regen, I don’t know.

And you’re correct...DPF cleaning process consumes Diesel, SCR consumes DEF.


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## firehawk618 (Feb 24, 2013)

Rivergoer said:


> Good point.
> 
> I’m no mechanic or GM engineer so I cannot state it’s a “known fact” the Gen 1 and Gen 2 DPF/DIC warnings work the same.
> 
> ...



I had timed the last 2 regens my car did. They both activated while cruising on the highway. They both completed in <7 minutes.

I suppose those that never let their car warm up fully, do lots of very short in town trips etc will see lots of aftertreatment issues.

I hope the 2nd gen displays a message in the DIC after a failed regen stating to leave the car running / idling until it's done.


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## Rivergoer (Mar 30, 2017)

I wonder if age/# of cycles affects regen time?

My Gen 1 at 97k miles and 200 successful regen cycles takes about 15-20 minutes at highway speed (approx 15 miles or so). 

Ive also noticed if I come to a stop the regen will pause (scangauge shows “0” instead of “1”) and regen won’t restart until EGT gets back up to 1100F. 

So in my case, idling the car during an incomplete regen won’t allow it to finish, I have to keep driving to maintain high EGT.


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## Diesel4Ever (May 30, 2018)

firehawk618 said:


> DEF is injected POST DPF and POST SCR. DEF is the last part of the after treatment system.
> 
> It does nothing but reduce NOx levels. That's it.
> 
> ...


On my 2.8 Duramax Canyon the DOC and SCR are both pre DPF. The DEF is injected after the DOC before it hits the SCR. The DPF is the final stage of treatment.

https://sandyblogs.com/techlink/?p=5403


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## firehawk618 (Feb 24, 2013)

Diesel4Ever said:


> On my 2.8 Duramax Canyon the DOC and SCR are both pre DPF. The DEF is injected after the DOC before it hits the SCR. The DPF is the final stage of treatment.
> 
> https://sandyblogs.com/techlink/?p=5403



Good info. Thanks for linking that.

I have yet to own or work on one that's configured on that order.


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## johnmo (Mar 2, 2017)

firehawk618 said:


> I suppose those that never let their car warm up fully, do lots of very short in town trips etc will see lots of aftertreatment issues.
> 
> I hope the 2nd gen displays a message in the DIC after a failed regen stating to leave the car running / idling until it's done.


In 43k+ miles I've not seen anything at all in the DIC about regens.

But my daily commute is over 50 miles each way, so it gets plenty of opportunities to complete regen cycles. One would think that sooner or later I'd catch one right at the end of my commute, but maybe it's smart enough to abort and retry on the next trip without causing any issues.


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## firehawk618 (Feb 24, 2013)

johnmo said:


> In 43k+ miles I've not seen anything at all in the DIC about regens.
> 
> But my daily commute is over 50 miles each way, so it gets plenty of opportunities to complete regen cycles. One would think that sooner or later I'd catch one right at the end of my commute, but maybe it's smart enough to abort and retry on the next trip without causing any issues.


I agree that if unmonitored you'd think that eventually you'd end up interrupting one.

Maybe I'll interrupt one intentionally on my car once to see if it does anything.


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## Barry Allen (Apr 18, 2018)

Diesel4Ever said:


> On my 2.8 Duramax Canyon the DOC and SCR are both pre DPF. The DEF is injected after the DOC before it hits the SCR. The DPF is the final stage of treatment.
> 
> https://sandyblogs.com/techlink/?p=5403


That's definitely very interesting. I was assuming the DPF came first because manufacturers wanted the cleanest (lowest soot) exhaust possible before the SCR to keep soot from coating the catalyst there and possibly interfering with operation.


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## Diesel4Ever (May 30, 2018)

Barry Allen said:


> Diesel4Ever said:
> 
> 
> > On my 2.8 Duramax Canyon the DOC and SCR are both pre DPF. The DEF is injected after the DOC before it hits the SCR. The DPF is the final stage of treatment.
> ...


Yes it’s definitely a different layout than the other DOC/DPF/SCR configurations I’ve seen in light trucks.

Maybe the diagram is labeled wrong? Could be possible I suppose.


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## Barry Allen (Apr 18, 2018)

Diesel4Ever said:


> Maybe the diagram is labeled wrong? Could be possible I suppose.


It seems weird because you want exhaust to be as hot as possible (to a certain extent) to occasionally regen the DPF. DEF injection cools the exhaust because the water is flashing to steam. I suppose it's possible that DEF injection is disabled during DPF regen because exhaust treatment systems are allowed to be disabled for limited time periods for specific reasons such as that.


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