It’s a known issue with GM trucks from what I understand.
The def tank utilizes electronic resistance sensor. depending on the temp/humidity where you live, def crystallizes on the sensor and shows as if the tank is full/half, even though the actual level is lower. Eventually the crystal melts and all of a sudden you see a significant drop in the bars.
Best is to track the mileage and add accordingly.

I usually get about 2.5k/ 2.5G. My truck idles quite and bit.

 

I have a 2021 3500HD Denali SRW. A few weeks ago, I received the 1000 Mile Left DIC message about my DEF fluid level.
Right now, I am seeing 2 bars left on my DEF gauge. Should I be receiving another DEF DIC Mileage message before my DEF Tank runs dry?

 

I just wait till I get the 1st dash warning, then dump in 2.5 from Walmart and motor on…
keeps it fresh but not over full. Lasts about 5k miles….

 

Since purchased the truck have get track of mileage between filling tank also. When get about 1 bar below half, put 2.5 gal in which takes it back to full which is about after 6K miles. Just for grins, talked to service writer about this level problem, who naturally, first question was if using GM branded DEF fluid. Had heard that there is only a single place that makes this fluid and just puts different labels as it comes off the assembly line. Did not inquire about price from dealer but also concened about how "fresh" the fluid might be. Read again that do not want to store some this because of this shelf life and definitely do not allow it to freeze and then thaw. Gonna be doing some more reading up about this fluid.

 

DEF freezing and thawing doesn't harm it, it happens all the time up here in the great white north in the winter. However, getting it too hot and especially placing the container in direct sunlight will degrade it much faster and it will not have a 1+ yr shelf life...

 

The ratio of urea and water used for DEF was specifically selected because it will freeze/thaw and the 2 components will stay mixed.
It does have a shelf life.
Every container is supposed to have a date code.

Freeze/thaw won't harm it. It freezes at 12F/-11C
It has longer shelf life when it is cooler.

There are lots of sources of the shelf life vs temp info.

 

Found another thread on this topic and one of the replies dealt with the "Premium" vs "Regular" def sold. Fell for the marketing and have been topping off with the "Premium" but will try just the "Regular" and see what happens. One of the people that responded stated that the "Premium" might interfere with the DEF tank level sensor. Worth a try at the lease.

 

Consensus on many sites is that premium has caused more issues than it has solved. I don't really see any advantage in using it.
You can't beat WalMart DEF for freshness and price. Used it for years with no issues.

 

Hey fellas
I finally received and installed my Idash.
First thing I did was set up the emissions related page.
It’s interesting, that the banks shows me the fluid tank level in %, I’m at 34%. However my dashboard still shows the tank as half full. Does This means the level sensor is working OK but the dash is not registering it right.
I wonder if GM has the programmed the scale or calibration wrong, because they do use the same set up for 6.6 which is equipped with much bigger DEF tank.
Or something else that I’m not able to comprehend yet. I would love any insights.

I’m expecting my next regen in a couple of days and see how the gauges react.

 

Hey fellas
I finally received and installed my Idash.
First thing I did was set up the emissions related page.
It’s interesting, that the banks shows me the fluid tank level in %, I’m at 34%. However my dashboard still shows the tank as half full. Does This means the level sensor is working OK but the dash is not registering it right.
I wonder if GM has the programmed the scale or calibration wrong, because they do use the same set up for 6.6 which is equipped with much bigger DEF tank.
Or something else that I’m not able to comprehend yet. I would love any insights.

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I’m expecting my next regen in a couple of days and see how the gauges react.

the def gage in the dash is a running average over time. if your towing the truck can easily use more def than the gage can keep up with.

on your I dash it is an accurate instant reading. however your have to be on flat ground and either traveling at steady speed no bumps or stopped to see the true level.

 

Rumor has it the DEF gauges are not very accurate...?? Regen really doesn't effect DEF level, but towing apparently makes it drink it like a drunken sailor. I have just under 5,000 Km on the ODO and I think I'm down only 1 DEF bar segment.

 

I now fill at bulk. I always find that it takes much longer for the first segment to go out than the others. (probably I fill above the GM intended 'full' level?)

I've also found that with iDash, the def level stays at 100% for longer than expected.

Chart in 3.0L supplement shows amount it should hold depending on number of segments on/off

We have no way of knowing how close a segment is to switching off.
Could be the one above just switched off, could be the highest one lit is about to turn off.

With 4 segments off, it could mean it will take 2 gal, or it could be about to switch to 2.5 gal.
In any case, the tank is rated at 5.3 -- so 1/2 isn't half.

fwiw, topped the tank off for a full baseline to measure usage,
5300 miles later it had given 922 mp
nest fill 7941 miles later 1438 mpg
next fill 7348 miles later 1470 mpg

total measured 20597 miles / 16.28 gal = 1265 mpg
I'm not sure why the first fill gave such a low mileage - except that it included bunch of winter warmups and running, that also gave lower fuel mileage that it averages now (see start of the fuel economy graph in LM2 economy thread).

 

Remember that the iDash is showing the 'raw' number that the truck is reading. (idash doesn't use it's own sensor)
As well as averaging, the def segment gauge thought to be trying to estimate the amount of range remaining.
Like the fuel range display, it will depend on recent rate of def usage.

When changing to towing and the usage of both drops sharply -- so range estimate drops sharply.

When close to empty, the idash number will move up and down during sharper turns or quick accel/decel.

 

About 1 week ago, I added 5 gallons of DEF when I had 2 full green bars left on the DEF gauge, and the gauge now shows Full.
I got nervous as I had not received any DIC messages after I got the initial 1000 miles to go message displayed about 1,500 miles prior to adding these 5 gallons.

 

The best way I handle this is DIC warning, add 2.5, repeat.... It's never over full, never has a chance to get old. and still can go about 6 months with no issues. There is no benefit in keeping it full and could actually hurt you if you don't cycle thru it fast enough...

 

I thought this thread interesting because of the in-ability of GM to provide us owners with a reasonable and dependable way to be able to monitor our DEF levels on our L5P's. I know the Banks Idash will provide percentagesl but does not match the factory readings. Out of curiousity I contacted Edge to see if it was possible for the CTS-2 to display the DEF level and here is the quoted Edge response I got:

"On certain years of Duramax, we can read DEF level. We cannot read the DEF level on L5P unfortunately. We had a 2019 Silverado 2500 as well that we would drive from Utah to California for CARB testing and seeing DEF level would have been nice to see but we were unable to get that gauge to work, unfortunately."

It makes you wonder if the info is available through the OBD2 port and Banks can figure it out why can't Edge? I guess in the big picture it really doesn't make much difference if the data being provided by GM is bogus anyway.

 

I have a 2017 and a CTS3 monitor. The DEF level reading that I see is marginally better then the factory readout of 'EF level OK' until it hits 30%. What I find with my CTS3 is the readout typically shows 38 or 39% when the tank is full then it does start to drop but seems to still be hit and miss but it does provide good numbers when the level is 33% - so you get a bit more of a warning but not much.

 

What amazes me is a company like Banks Engineering can figure out a way to be able to provide an accurate DEF reading but GM who sells you an 80K truck that depends so much on DEF they cant seem to do it.

On top of that once you get to a certain level GM locks you out of your info center so you cant even know how many miles you have remaining on a tank full of Diesel. Really Lame and another reason why Banks is so fantastic and one hell of a great aftermarket product provider. Even EDGE can make their CTS series give you a DEF level on the L5p. lol

 

On top of that once you get to a certain level GM locks you out of your info center so you cant even know how many miles you have remaining on a tank full of Diesel. Really Lame and another reason why Banks is so fantastic and one hell of a great aftermarket product provider. Even EDGE can make their CTS series give you a DEF level on the L5p. lol

That's misleading.
You still have a viewable fuel gauge.

Once the it thinks the tank is empty, it does put up a 'miles to speed limit' display in the dic area.
This display cannot be 'dismissed'.

This display gives a running countdown of the 'miles til speed limit' that updates mile per mile as the truck is driven.

I intentionally drove my '18 L5P to empty....

 

Since this is the LM2 section, LM2 owners should be aware that the LM2 only gives 50 miles to speed limit, instead of the 500 that the L5P gets (as shown above)


EDIT (Dec '22)
Pics in another thread, but it got to empty again, and this time the warning was 500 miles

 

Since this is the LM2 section, LM2 owners should be aware that the LM2 only gives 50 miles to speed limit, instead of the 500 that the L5P gets (as shown above)

Towing to/from northern Wi last year, my LM2 gave me a countdown well before 50 miles on both legs of the trip. Pretty sure it was at the 500 mile point since it was 700 miles each way. Did GM update our trucks without letting us know? Haven't towed that kind of mileage since then so I don't know if that changed.

 

Pulling this thread forward with a quick question. From what I have read it is better to run the tank to almost empty before putting new DEF in. In other words, you do not want to keep diluting the old def with new? I do 12 to 15k a year. I am at 3700 miles and my def tank is reading 1/2 and I should probably wait for it go down the 1 bar before adding 2.5 gallons?

 

You can do it either way.

 

I read a post somewhere where the guy states that you shouldn’t run the tank lower than 1/2 because of the white residue powder that can form… like what you see on the jugs when it dries. Makes some sense I guess. I don’t think the DEF will go that bad when in the tank. If you have a banks iDash gauge you can also monitor the DEF concentration level…

 

I believe that 'theory' is incorrect, although it does get suggested from time-to-time.

If water separates /evaporates inside the tank, the water is still inside the sealed the tank
Crystalized urea (the non-water component of def) easily remixes with water. (wouldn't be hard to test)

Fwiw, last 2 trucks (and the plan for current one) I almost always run the def tank to empty (just for shits and giggles) and then fill completely full from a bulk def pump.

Truck prior to those I wasn't near a bulk location.
I would purchase and add def after the 1000 mile warning -- so that tank was never more than about 1/2 full. (the method that @Stbentoak described).


If you were to search old def threads started back in 2011 when we first had def, there were 1000's of posts about the trucks being unable to rest the levels after adding def. (lots and lots of theories were tossed out)
For a period of time late winter/early spring, GM was updating the programming every 2 weeks trying to resolve the issue.
Start of 2012 used 'finalized' programming. Fall of 2012 all '11's were to be updated to that finalized revision if they hadn't already received it.

The 'def quality poor' fault was also very common on early LML's.
It turned out to caused by faulty NOx sensors drifting from correct calibration. Sometimes they drifted back in, and so sometimes it incorrectly seemed as if work on truck had corrected the problem.
They didn't all do it. Eventually it was determined the sensors were the issue and they were modified.

Later production had the revised sensors.
Trucks with the early sensors were given an much extended warranty on those sensors.


Despite often running to empty, I've not had a def issue since having a NOx sensor replaced early in the period I ran the 2011.

 

Run it down till you get the first warning on the DIC. Put in 2.5 from walmart….wash, rinse, and repeat and you will never have a problem.

 

Run you DEF down as far as you can. Then when you get the warning 100 miles before reduced speed add some new stuff. Only down side is that once you get the low def warning all of your DIC functions (ie mileage, ranges, ect.) all get locked out. If you follow this suggestion you will never end up in a GM dealership with a DEF low quality warning. I will say the L5P is much better dealing with old DEF then the LML was. Then again the L5P drinks a great deal more of it.

 

We don’t have any def tanks in Canada we have to buy them in a 2.5 gallon jug usually I just wait till my def tank shows half then I can add a full jug in. Been doing that since I bought it and haven’t had any def issues.
I was told it’s good to keep it full especially in winter it gets below -40 here

Seems like everyone has a different theory I don’t know what’s right or wrong.

Edit; not sure if it makes any difference but I have an LM2.

Sent from my iPhone using Tapatalk

 

We don’t have any def tanks in Canada we have to buy them in a 2.5 gallon jug usually I just wait till my def tank shows half then I can add a full jug in. Been doing that since I bought it and haven’t had any def issues.
I was told it’s good to keep it full especially in winter it gets below -40 here

Seems like everyone has a different theory I don’t know what’s right or wrong.

Edit; not sure if it makes any difference but I have an LM2.

Sent from my iPhone using Tapatalk

I'm in Canada.
We do have bulk stations.

I've been using bulk pump at truckstops for at least 5 years, and I know it was available prior to that.

Fleets, farms, construction users often have DEF in bulk totes that have pumps. Fuel distributers near you can likely supply DEF if totes if you want.


Be a little careful in winter.
Not sure if this has changed with the side fill system in use now, but the engine compartment fill pipe used for so many years isn't as flexible as the tank could be damaged by DEF freezing.
If the added jugs don't completely fill then this is not a concern.

 

For the amount of DEF I go through in a year I’ll just buy the jugs, go through max of 3 a year. The LM2 seems to sip DEF in regular, non towing driving.

 

I like to keep mine on the low side in our Canadian winters. I don't like the warning so just add one jug when it is below 30% (when at 30% it will take 2 - 9.46L jugs to fill). I may be wrong but aside from the expansion when DEF freezes, my thinking is that it takes more energy to thaw the frozen DEF and the more that has to be thawed, the more load put on the heater.

 

I like to keep mine on the low side in our Canadian winters. I don't like the warning so just add one jug when it is below 30% (when at 30% it will take 2 - 9.46L jugs to fill). I may be wrong but aside from the expansion when DEF freezes, my thinking is that it takes more energy to thaw the frozen DEF and the more that has to be thawed, the more load put on the heater.

Do you know if the heater shuts off once it’s unthawed or if the heater stays on once the truck notices temps below X
I just figured it was always on under certain temps.

Less to thaw does make sense.


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I’m programming this into my Banks gauge so I can monitor this winter at what temperature the heater comes on and what temp it maintains. My guess is it adjusts voltage to the heater to keep it at a somewhat constant/consistent temp, but that’s just a guess.