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Discussion Starter #1
When I monitor my DEF tank level while driving i notice that tank level steadily decreases at a rate of about 1% per 60 to 70 miles traveled whether its in regen or not--I am wondering if this is the way the design is supposed to work or not?? Is DEF used constantly or is it only supposed to be injected during regen??
This is my first diesel and I bought it used--is it possible that there is some kind of tune installed that modified the way this system works? The truck feels very strong to me but the only thing I have to compare it to is my 5.3 liter half ton Silverado...

Thanks for any info ya'll can share.
Rick
 

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Rick,
How are you measuring your DEF usage? I have NO way of knowing how much is in my DEF tank on my 2017 GMC Denali.

DEF is used constantly....and probably more so during a REGEN.

Thanks,
Mike
 

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Regen and def usage are independent of one another. Def usage is directly correlated to fuel usage. I could be wrong but I don’t think def usage goes up during a regen. At least on an L5p. Def usage should be 1 to 2% of fuel usage. So if you go through 100 gallons of diesel you should use 1 to 2 gallons of def.

That’s why guys always ask the question after their first tow. Fuel mileage goes down and it seems def usage goes up. It only seems like you are using more because you are also getting lower mpg of diesel while towing.

If I burn 100 gallons of diesel at 20 mpg, I’ll go 2000 miles and use 2 gallons of def.

If I burn 100 gallons of diesel at 10 mpg, I’ll go 1000 miles and use 2 gallons of def
 

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MIkey52 - it was my understanding that on my LP5, during a REGEN, the system uses more fuel to create the additional heat needed to burn away the particulate build up....therefore, DEF usage would go up.

Am I wrong?
 

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I don’t know for sure as def is injected further up stream than the dpf. The def, I believe is injected to reduce the nitrous oxides produced by combustion in the cylinders. I don’t think the def would get to the dpf to make any difference. I forget the sequence of events but MrWizard posted a really good post as to location of the injection points. Earlier models didn’t have a 9th injector. So they may have used more def in a regeneration.
 

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GM published a document when the LML was introduced indicating that DEF usage was about 1.25% of fuel usage.

Meaning 100 gallons of fuel would be about 1.25 gallons of DEF.


DEF is injected before upstream f the dpf, but yes, it is for reduction of NOx.

The DPF catches soot, not Nox.
Regen is to burn the soot from the DPF.

Fwiw, the LMM (07.5 thru '10) was equipped with a DPF, but did not use DEF. DEF added in '11 because of the reduced permissable level of NOx, as the emission requirements tightened.
LML, (2011), also introduced the extra fuel injector into the exhaust so the 'excess' fuel for regen did did not pass thru the engine.
 

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Rick,
How are you measuring your DEF usage? I have NO way of knowing how much is in my DEF tank on my 2017 GMC Denali.

DEF is used constantly....and probably more so during a REGEN.

Thanks,
Mike
When the DEF level is below 30% remaining, the DEF level page in the DIC will change from the 'DEF OK' message to a 'DEF % remaining' message. (for trucks from 2012 thru 2019).
2011 did not have this DIC page.
2020 has a def 'gauge' that provides additional level information (but has been reported to have accuracy 'issues')
 

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Discussion Starter #8
Mike, On my 2013 LML when I scroll through the data on my info center-which is a blue led display located in the lower portion of the tach--there is a display that shows DEF tank level. I drive 40 miles to work one way and as I drive I can monitor this and see that level decreases about 1% per 60-70 miles.
Rick
 

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Hi I have a 2016 lml, i wait till my % gauge gets down to around 16% usually (unless I'm going some where with camper and around the 20% range) then i go to a truck stop that has def bulk aka at the pump, then fill up, right down miles and exact gallons and I'm averaging 1100-1600 miles per gallon of def, which is around 6000 miles, it is nice to keep track of usage for reference purposes. Def at pump where im at is around 2.759-2.809 a gallon heck of alot cheaper then buying a 2.5 gallon jug.

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GM published a document when the LML was introduced indicating that DEF usage was about 1.25% of fuel usage.



Meaning 100 gallons of fuel would be about 1.25 gallons of DEF.





DEF is injected before upstream f the dpf, but yes, it is for reduction of NOx.



The DPF catches soot, not Nox.

Regen is to burn the soot from the DPF.



Fwiw, the LMM (07.5 thru '10) was equipped with a DPF, but did not use DEF. DEF added in '11 because of the reduced permissable level of NOx, as the emission requirements tightened.

LML, (2011), also introduced the extra fuel injector into the exhaust so the 'excess' fuel for regen did did not pass thru the engine.
Regen is to burn soot to ash and stays trapped in dpf and eventually the dpf needs to be cleaned or replaced, the the class 8 trucks im around the dpf's are scheduled to be cleaned around the 250,000 mile mark, not a big fan of def or dpf systems, a majority of problems with the those big trucks is emissions systems not engine systems and idle time on them is a killer but trying to tell a driver not to idle when its hot or cold doesn't go very far.

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