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Hello all,

2017 LTZ with about 34,000 on the clock. I was recently towing and the DEF message popped up and stated I had 1000 miles left. Great, totally normal. It stated counting down percentage wise like it should and was down to 25%. Two days ago I looked at and it is now reading "ok" on the amount even though I have not added any. Generally, I wait until I get to 15% as I know that I can safely add about 6 gallons and the old stuff is used up.It has not done this before.

Here is my question:

Is this normal to do this?
Anybody else have this happen?
Shouldn't the gauge only read "ok" once to is above 30%?
Will the message reappear?
Why is it thinking that DEF has been added?
Is there a way to reset it?

Any input would be appreciated.

Thanks for your replies.
 

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Assuming the L5P def level detection is similar to the LML it's just a series of 'pin sensors' and some software that guesses the level between the pins --- not very accurate. (I understand that a similar pin system is used on RV tanks).
Probably also why they didn't install a gauge ?

DEF usage goes up/down when fuel usage goes up/down. DEF range estimate is like fuel range estimate -- both can only be accurate if running steady engine speeds/loads

I've also had mine go from a 20 something % remaining back to an OK display. But this was not after the 1000 mile warning.
Mine has given the 1000 mile warning somewhere around 20%
(only refilled twice so far; just checked - it's about 6000 miles since last fill and is at 23% - probably see it again soon)

1000 mile only appears once.

When it gets to about 300 miles remaining it will give a 'miles til empty' message -- and it each key cycle after that will again give the remaining mileage.


Remember that it is miles to empty -- not miles to speed limit.

When it reaches 'empty' there is a Exhaust Fluid Empty Refill Now' message
and a '500 miles to 65 mph limit' warning.
Then 75 miles til 55 mph limit
Then 75 miles to 5 mph limit


Last fill I (intentionally) took it to empty.
I gave the messages as advertised.
What I also found was that the messages will not clear -- meaning the DIC pages couldn't display other dic info -- which was annoying (and probably intentional). Of course gauges and speedo all still work fine.

I was doing all local running and was going to run til the 65 mph limit, but the non-clearing screen changed my mind.
I got to watch the screen til the next convenient bulk location.

At 50 or 60 miles after the 'empty' message, the 7.0 gal tank took 6.3 gal (26.5L tank took 24L)
 

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Well I am disappointed in the crap GM puts out with respect to the so called DEF Gauge. Does not work well at all. On my trip to the ranch Monday had about 1600 miles on the 2020 bored on the highway scrolling through the DIC and Oh My DEF at 50%! Hmmmmm so watched it for another couple hundred miles and when I stopped for fuel thought ok fill it up took less than a gallon before overflowing and making a mess! Went back to full when I started the truck back up--took about 5 minutes to go all the way to full.

Lesson here is always carry DEF and use the odometer because the crap GM system does not work well.. Other than that great...
 

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There is a software update that supposedly helps with this, it also supposedly resolves the random "DEF fluid empty - reduced speed in blah blah"
 

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Well I am disappointed in the crap GM puts out with respect to the so called DEF Gauge. Does not work well at all. On my trip to the ranch Monday had about 1600 miles on the 2020 bored on the highway scrolling through the DIC and Oh My DEF at 50%! Hmmmmm so watched it for another couple hundred miles and when I stopped for fuel thought ok fill it up took less than a gallon before overflowing and making a mess! Went back to full when I started the truck back up--took about 5 minutes to go all the way to full.

Lesson here is always carry DEF and use the odometer because the crap GM system does not work well.. Other than that great...
2020 is a different animal than the '17 - '19
(different tank, different type display, presumably a different type of sensing in tank ; sounds like it's not necessarily better, just different)

IMO, no point in carrying def. With all the warnings before it's empty, and 500 miles after it's empty just add some the next time it needs fuel.
 

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Some of us had '11's and were able to manage def without any gauge, just the warnings and odometer.

It can still be done that way....
 
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2020 is a different animal than the '17 - '19
(different tank, different type display, presumably a different type of sensing in tank ; sounds like it's not necessarily better, just different)

IMO, no point in carrying def. With all the warnings before it's empty, and 500 miles after it's empty just add some the next time it needs fuel.
Normally I would agree about carrying the DEF had it from my Ford before I traded it. HOWEVER---My 2020 manual does not speak of a 500 mile after it's empty grace period. Maybe your older models do but the new ones it does show the gauge and the corresponding bars and how much DEF can be added. Where mine was it showed to be 2.5 gallons low. It does stand to reason that the gauge and maybe the limp mode system works off of that as well. Bet you would feel pretty silly if the gauge malfunctioned and you still had half a tank of DEF and you were limited to 5mph in the middle of nowhere.

Point of my post and just for me I will never trust the DEF gauge and as long as I have this truck which will be a couple of years will have a box of DEF in the tool box. :) The only reason I went back to GM was they made the 4x4 a good truck again. Where I drive (SE NM oil patch) you do not see a lot of oil burner GM 4x4's because of the location of the DEF tank. It was placed in the worst possible place there is for a truck that has to go off road. Have seen more than one that had to be towed in..
 

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Normally I would agree about carrying the DEF had it from my Ford before I traded it. HOWEVER---My 2020 manual does not speak of a 500 mile after it's empty grace period. Maybe your older models do but the new ones it does show the gauge and the corresponding bars and how much DEF can be added. Where mine was it showed to be 2.5 gallons low. It does stand to reason that the gauge and maybe the limp mode system works off of that as well. Bet you would feel pretty silly if the gauge malfunctioned and you still had half a tank of DEF and you were limited to 5mph in the middle of nowhere.

Point of my post and just for me I will never trust the DEF gauge and as long as I have this truck which will be a couple of years will have a box of DEF in the tool box. :) The only reason I went back to GM was they made the 4x4 a good truck again. Where I drive (SE NM oil patch) you do not see a lot of oil burner GM 4x4's because of the location of the DEF tank. It was placed in the worst possible place there is for a truck that has to go off road. Have seen more than one that had to be towed in..

I wouldn't have done the test if I was going to be in the middle of nowhere -- and I wouldn't let it get low enough that I need to add some if I was going to be in the middle of nowhere.
Point kinda is that given say a 500 or so mile fuel range and 1500 or so miles of warnings and def available pretty much everywhere there is fuel....

If course if the truck is carrying extra fuel, then perhaps extra def is a good idea. Or be sure def tank has enough to match the fuel carried.

I downloaded a copy of the 2020 diesel supplement --- and it just says there will be instructions and that a distance til speed limited warning (instead of all the extra info in previous year versions)

2020 manual:
If the DEF low warnings are ignored and the DEF tank becomes empty,
the DIC will display messages that describe the action needed and
distance until vehicle speed is limited.



We need a volunteer to carry a jug and then run it til empty to find out what the warning says.


Of course it's a lot simpler to just add some whenever it gets down to say 20 or 25% remaining.
 

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I have a 2020, I got a 1000 mile and a 300 mile warning. Which were only about 150 miles apart for some reason. I was towing I guess.
 

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FWIW, we have DEF gauges on our fire trucks and they are no better than the "OK" or DEF low on the GMs... They say 1/4 full and you get 2.5 gallon in and they over flow... Its a DEF conspiracy ....
 

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My 2020 has done and is doing all of the erroneous DEF messages. I am at 1500 miles. Is the update out? When will it be out? Where are all the fancy gas station with DEF at the pump, I am not seeing it in Colorado but I am rural.
 

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The DEF gauge is also annoying from the standpoint that it allows dealerships to skimp on DEF. Since it just reads OK above 30% they can claim they filled it and the average customer has no way of checking. My truck hit 30% on the gauge at 800 miles, meaning that the tank was less than half full when I rolled off the lot. When I went in for my one free maintenance from GM they once again lied about filling the DEF.

I bet that most people reading this forum do their own maintenance, but think about how many average customers go pay the $100 or whatever for a service and expect fluids to be topped off. These are very expensive trucks and yet dealerships cheap out on DEF thanks to GM's ridiculous "gauge".
 

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The DEF gauge is also annoying from the standpoint that it allows dealerships to skimp on DEF. Since it just reads OK above 30% they can claim they filled it and the average customer has no way of checking. My truck hit 30% on the gauge at 800 miles, meaning that the tank was less than half full when I rolled off the lot. When I went in for my one free maintenance from GM they once again lied about filling the DEF.

I bet that most people reading this forum do their own maintenance, but think about how many average customers go pay the $100 or whatever for a service and expect fluids to be topped off. These are very expensive trucks and yet dealerships cheap out on DEF thanks to GM's ridiculous "gauge".
They probably put a 1 gallon jug in it like they would in a cruze....


I'll give my selling dealer credit.

It was full at delivery -- and they also gave me a 2.5 gal jug.

Didn't use it til about 6800 miles. Dumped it in then topped it off at a bulk pump at a truck stop.
Next fill was about 13,900.
It's just under 20,000 now and showing 23% -- expect it'll give the 1000 mile warning soon.
 

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My dealer must have filled mine full. I've only had to fill it once and I'm at 13k on the odometer. I just wait for the warnings and top it off at my local truck stop. Not a big deal. I couldn't care less about the gauge.
 

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I have never gotten the 1000 mile warning on either my '11 or current '18. Generally just get the DIC warning of any where from 250 to 400 miles left. And yes that stupid guage is pretty useless.
 

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I had the DEF% as one of the 4 gauge readouts on my Banks iDash in our 2019 Chevy 3500HD.

It showed 40% to 42% when it was actually 100% full ... usually varied between 36% to 39% (who knows what the real % was)... and usually around 32% when I would see the initial DIC warning.

So the iDash readout only varied from 32% to 42% across the actual full range (well at least most of the full capacity range ... never ran my DEF tank dry or into the reduced speed range).

I have since replaced the DIC readout with more useful (and accurate) information like injection pressure.

Carry an extra gallon with me at all times that I throw in the tank if I am out of town and not near DEF availability ... also throw that 1 gallon in my tank every few months and replace it ... just to make sure it does not go bad from the heat in the summer.

Side Note: You all are getting much better (lower) DEF usage than me ... but I tow 10,000 lbs up hill in the Rocky Mountains on a regular basis ... and I have a serious lead foot issue too (per my wife and our RV friends).
 

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Been Using Distilled water , In My Rams and GM the Ram Years are 2013-14-15-16, the Duramax is 2015 , DEF is simply 67.5 Deionized Water and 35.5% Urea. I do start mixing the Urea about Now for winter Use it lowers the freeze Point at 33 % urea to 12F, I still don't run 33% ,I'm 10-17% makes it down to about 20F.

Back in 2015 I leased the equipment for tail pipe emissions, Fuel Analyzer, lets just say 95% of Driving DOES NOT NEED 33.5% to lower the NOx. The Urea is what plugs the DEF Injector and causes Most DEF Injector and Pump problems, Some Claim theirs sensors to Detect DEF %. LOL YEP IMO they just detect the Presents of Urea not the %. Yep generally 2 Sensors to Measure the NOx both are before the Mixing chamber, they Have Done away with the Ammonia Sensor Because it was soooooo problematic and inaccurate.

I also did My best to measure the NOx PPM that the other 5% of the time was higher than 0/1 I would need to Drive My truck 700,000 Miles to equal 1 lighting strike Its just a theory on How Much NOx is created by lighting strikes https://www.sciencedaily.com/releases/2009/10/091030100022.htm
 

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Yes..... its easy.... I been using Urea in other commercial Businesses for Years.... heck I know of many practicing the same as Me, Using Distilled water. Another Practice is just buy the 2.5 or 1 gallon DEF and just mixes it.. 50/50 or Go buy that 1 gallon Distilled Water at $0.89 a Gallon and NO Tax and dump it in...... I don't own LP5 or I would be running 10-17% Urea - Distilled/Deionized Water. I been Running Lower concentration of DEF for Years.. NEVER a DEF problem. On My Rams When the SCR were recalled and eliminated the Ammonia Sensor. My Mixing chamber were polish and My DEF Injectors on all of them perfectly clean. Spotless all at 20-40K Miles. Even when the systems had the Ammonia Sensor Na-da DEF Problem.
 
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