Unreliable DEF tank monitor in our GMC Sierra 3500 HD?

[MarkEHansen]

We recently purchased a 2019 GMC Sierra 3500 Denali HD with the 6.6L Duramax TD engine.

After just around 100 miles or so, we got a warning in our driver's information center (DIC) that we only had 340 miles left on our DEF tank. The owner's manual says that a full DEF tank should last around 5000 miles and the first warning should come when there is 1000 miles left - so we assumed the tank was nearly empty.

I had planned on picking up a couple jugs of Blue DEF, but noticed the warning went away. I navigated to the DEF Tank Status page in the DIC and it now shows the DEF Tank as "OK".

Are these tank monitors really that flaky, or do I have a warranty issue?

Thanks,

[jimthemosaicguy]

Check for a recall. I have a 2015 gmc 3500 diesel Denali long bed dually that did the the same thing after 1,000mi. Then it would drop to 350mi warning.

I’d start to refill the tank and it would only need 1 box of blue def. Took it in. The dealer repaired no charge. No problem since then.

[mikec557]

We recently purchased a 2019 GMC Sierra 3500 Denali HD with the 6.6L Duramax TD engine.

After just around 100 miles or so, we got a warning in our driver's information center (DIC) that we only had 340 miles left on our DEF tank. The owner's manual says that a full DEF tank should last around 5000 miles and the first warning should come when there is 1000 miles left - so we assumed the tank was nearly empty.

I had planned on picking up a couple jugs of Blue DEF, but noticed the warning went away. I navigated to the DEF Tank Status page in the DIC and it now shows the DEF Tank as "OK".

Are these tank monitors really that flaky, or do I have a warranty issue?

Thanks,

Mark

For what it's worth, we have a new 2018 3500 Z71 Duramax (almost Denali, LOL). we didn't get the 350 mile warning but we did get a low def warning sooner than we should have. Turns out GMC has a service bulletin, or so I was told by a small town dealership, that told dealers to top up the def bec some left the factory with a low level. Aside from that and a few thousand miles later, we got a low def warning. The computer that tells you how many miles you have left of def seems to calculate "non-towing" miles. As we pulled our 5er and got the first warning, the estimated mileage fell far faster on the subsequent warnings. Finally got to a truck stop and bought some def. Now we keep a 2.5 gallon box in the back of the truck. Sure wish it was easier to pour in... and easier to know how much to add.

Mike

[Javi]

Do the GM trucks not give a less than half warning on the DEF?

Do the GM trucks not have an information scroll that reports DEF levels?

Just curious....

[mikec557]

Do the GM trucks not give a less than half warning on the DEF?

Do the GM trucks not have an information scroll that reports DEF levels?

Just curious....

The first warning comes on and says you have x miles to go. If you scroll thru the display you'll see you have 30% def fluid remaining. If you're towing you won't get as many miles as the warning message indicates. If you're above 30% fluid the display simply says "def fluid level ok". Not very informative with an approx 7 gallon def tank.

[Javi]

Huh... Ford says Less than 1/2 ... I've never seen any other warning, although I know they exist. I always pour a 2 1/2 gallon bottle in within a couple of hundred miles of the first warning.

Been doing that for roughly a 100K and two trucks...

But my dually is my daily driver.

[MarkEHansen]

Well, mine said 30% remaining and now it reports OK without adding any DEF. I was not towing when I got the 30% remaining warning.

Was the GM service bulletin just that the factory didn't fill the tank, or was there some mechanical/electrical problem which had to be resolved?

Thanks,

[MarkEHansen]

By the way, the GMC owner's manual says that when we get the first 1,000 mile warning, the DEF tank should be ready for about 3.8 gallons. My "plan" was to put in 2.5 gallons when getting this warning. We'll see what happens.

[mikec557]

...
Was the GM service bulletin just that the factory didn't fill the tank, or was there some mechanical/electrical problem which had to be resolved?

Thanks,

I didn't see the bulletin. The service writer just grumbled the dealership I bought the truck from should have done it. As it was, they said they filled it but didn't... because later that same day I got the warning and poured 2.5 gallons in. They also didn't rotate the tires as I asked and as they say they did. For what it's worth, don't use the only Chevrolet/GMC dealership in Yulee Florida.

[mikec557]

By the way, the GMC owner's manual says that when we get the first 1,000 mile warning, the DEF tank should be ready for about 3.8 gallons. My "plan" was to put in 2.5 gallons when getting this warning. We'll see what happens.

That's a good plan. We have 10,000 miles on it now and always carry def. My experience above was before I learned what to expect from def consumption.

[MarkEHansen]

I don't plan to carry it because it gets old and I think I'll have plenty of time to find a Walmart when I get the 1,000 mile warning. We'll see how that plan works...

[Javi]

I don't plan to carry it because it gets old and I think I'll have plenty of time to find a Walmart when I get the 1,000 mile warning. We'll see how that plan works...My DW is in Walmart at least twice a week, so I just ask her to add a jug to her shopping list when I see the less than 1/2 warning..

[mikec557]

I don't plan to carry it because it gets old and I think I'll have plenty of time to find a Walmart when I get the 1,000 mile warning. We'll see how that plan works...

We're full timing and I can say sometimes there's a nearby Walmart and sometimes not.. And since we tow so much it's easier to have the DEF on hand. I'm pretty sure you will not get a 1000 towing miles but I can't back that up with data. I guess time will tell.

[MarkEHansen]

Yes, I'm really curious about that. The book says I can get around 5,000 miles, but that's non-towing miles. This is my "2nd" driver - as I primarily commute using my motorcycle, so it's going to get about 70% commute and 30% towing (I think).

... until I start getting more vacation time :)

[PARAPTOR]

My DW is in Walmart at least twice a week, so I just ask her to add a jug to her shopping list when I see the less than 1/2 warning..

Similar here, since there is no indicator on the Chevy I have, when I see it on sale I buy a couple jugs. Then every now and then I will top it off, usually takes one jug. Not sure why there is no way to check how much is in there, only that warning message. Only seen message once thought it indicated xx hundred miles remaining ??? If I recall took 2 bottles ~ 5 gal

[hdrolling]

The L5P GM trucks with the 7 gal DEF tanks don't have a float level sensor, there is no level “float”. The level works exactly the same as an RV water tank. A couple of electrodes spaced vertically at different levels and a common ground at the bottom.

Conductivity between a level electrode and ground means level is at least that level, and less than the next higher level electrode, but the ECU has no idea where in that range.

Hence the step wise level reduction “OK” until “30%” etc. If you read the PID with a scanner from the OBD port you can actually see the level steps (82% down to 44% etc, and you can see the level fluctuate when turning. )

The lower level % countdowns are only predictions based on usage. This also explains why a DEF addition may not read on the DIC or clear a speed warning. If not enough is added to reach the next higher level electrode the ECU is none the wiser. Clear as mud right?

[travelin texans]

My '13 GMC holds 5.3 gallons of DEF & will hold a 2.5 gallon jug at about 3000 to 3500 miles, towing doesn't seem to increase usage.
I have a 131k miles on my truck & have never carried extra DEF. The warning comes on "1000 miles left" which is less than 30% & have never
had any issues with running out, never gotten bad DEF & even while towing never gotten below about 20%.
I have a friend with a Ram diesel & claims while towing he has to fill DEF about every fuel fill up or may run out.
My DEF gauge works much better than any of the holding tank sensors on my rv, it may not be accurate, but the percentage does change whereas the ones on my rv NEVER change, they've read the very same as the day I towed it off the dealers lot 6 years ago.

[Frank G]

IMHO I would fill the DIF to the top, and NOT carry a spare in the truck waiting to spoil. Def is available at every station that sells diesel and your GPS is programmed to pass every Walmart along the way. My 16 Cummins uses about 1 gal/1500 miles empty and 2.5 gal/1000 miles heavy loaded, I doubt your GMC is much different. DEF spoilage is dependent on temperatures, the higher the temp the faster the spoilage rate. Stored in the bed of the P/U under a Tonneau cover is a recipe for disaster. Again, this is my opinion, do as you like.

[Wyldfire]

Ford's owner manual specifically stated do not fill to the top as DEF will freeze and expand. When this happens the tank will crack.

[JRTJH]

Here's a question about "dilution":

If you have water in your fuel, do you drain the tank, then refill or do you keep topping it off every time it gets below 3/4 full, until the tank is "finally purged" ???

Relate that to the DEF tank: If you consistently "top it off" every time it gets close to half, in reality, what you're doing is diluting the "old DEF" with "fresh DEF" over and over. Theoretically, doing it that way, if you fill every 6 months, then around 25% of your DEF is older than 12 months and 12% is older than 24 months. On a truck that only gets driven 5,000 miles a year, the DEF tank may not reach 1/2 full for over a year. Filling it on that schedule, 25% of the DEF would be 4 years old and still in the tank.

The Ford website (I'm not sure about the diesel supplement to the owner's manual) suggests allowing the DEF tank to fall to the "lower level notices" before refilling the DEF tank. Most dealerships will top off the DEF tank at oil changes. Their DEF is in a 55 gallon barrel and in smaller dealerships, that barrel may be 6 months or older. IMHO, that's "old DEF" and I don't want my tank filled with "old DEF" if it only needs 1 or 2 gallons.

In order to "cycle DEF out of the tank, it needs to be injected into the exhaust system. That only happens to "nearly all, or "most of the DEF" is used and the tank is allowed to reach "lower levels". If the truck only gets 5K or 10K a year, it may be 2, 3, or 4 years before that "stale DEF" is injected into the exhaust system. Again, IMHO, that's not good for the exhaust system and is an invitation to emissions problems. On a truck that gets driven 10K-15K miles a year, it probably doesn't matter much, but I wonder how many trucks that get driven "only during vacation" and typically less than 5K a year,will develop DEF problems that stem from "stale DEF" which is really "owner caused" ????

[AbHDToyHauler]

My 2018 came up pretty quick too when i first purchased it. I am pretty sure the dealership only put in enough to get the warning off. Once I topped it up it has been "normal" and I guess accurate. Obviously it calculates the def useage based on fuel used as when towing it uses it much faster . Even when its low if you read the message carefully it tells you that if you don't put fluid in you will have like a 600 miles before it goes into limp mode. (Don't quote me on the mileage to limp mode as i'm pulling it from memory and my memory is awful).

[tundrwd]

I don't plan to carry it because it gets old and I think I'll have plenty of time to find a Walmart when I get the 1,000 mile warning. We'll see how that plan works...

I'd be careful with counting on that. Depends on where you go, but where I live, the local Walmarts have been "wiped-out" from time-to-time of DEF fluid. None on the shelf. It'll be there in a couple days, but that doesn't do you much good when you're "passing through". You don't get a lot of towing miles before the computer tells the truck to just quit. And that's that. You're dead on the side of the road. GM doesn't have a "no start" idea - once it says it's out - it starts reducing the speed you can drive (farther you try to travel the slower it goes), and I think it's only about 50 miles total once you get the "no fluid" warning and it just stops. Period.

You can always see about a truck stop - they normally have DEF fluid dispensers, and because truckers will use it - it's usually pretty fresh.

Although - Car and Driver says DEF fluid doesn't deteriorate over time https://www.caranddriver.com/news/a15342943/what-happens-when-the-diesel-exhaust-fluid-tank-runs-dry/ - that does NOT seem to be the consensus of many - but that's what Car and Driver say.

I've kept a 2.5gal box of DEF fluid in the back of the truck for up to about 5 months with no issues. It's always used within 3-4 months (I don't let the warning light come on, I just get to a point, and drop the 2.5gal box in).

Good thing about having the store "wiped out" is that you have some feeling that it's "fresher" than when it's been sitting there a lot (if that counts). So I tend to go to Walmarts in semi-rural areas where farmers and ranchers, etc. go. I've seen those guys buy 4-5 2.5gal boxes of DEF fluid at one go.

[takpak]

We just had the "engine warning" light come on recently on our 2015 GMC. It's 4 years old with 28,000 miles on it. As to the first part about new and being filled, probably not. The dealership we bought from claimed to have filled it.....NOT. The dealership I use for service (very good one) had to fill it shortly after purchased, and it took almost 5 gallons. I recently got the recall notice on the tank sensor. Sure enough, not long after the warning came on. The dealer reset, and said try for a bit. A week later it was back. So, sensor was replaced under warranty. Now, one thing the service manager said, was to stay away from the Blue DEF. He said they've had a lot of trouble with store bought Blue DEF causing failures. Coincidentally, I had just had to put 2 gallons of Blue DEF in, as I was on the road and it was getting very low. Shortly after that, I had the warning activate. Coincidence, or???? GM uses a kind of "amber" colored DEF, and that's what they recommend. I will have to say that almost 4 years of dealer installed DEF, no problems. I put a bit of Blue DEF in, and the problem occurs. For me, I'll let the dealer fill it now. Then I know I have full warranty coverage!

[MrEnto]

My 14 F350 had some false DEF readings. After much discussion with mechanics and a friend in the equipment industry (having DEF issues), we sort of concluded that keeping the def tank full was the way to go. Def leaves behind that crystalline residue as it dries out. I see it around the fill spout. We surmised that these crystals in a low tank interfere with the sensor reading. Keeping the tank full keeps the crystals from forming. My ford sensor is supposedly like a fuel tank sensor and not an rv tank sensor so the crystals may cause the false warning. Since practicing “full def tank”, no issues. Just my opinion..

[MarkEHansen]

How are you supposed to know how much to put in? Assuming I want to fill it, I know that the tank takes 7 gallons, but I don't know how much is still in there. I just looked at the DEF fill tube and it is black plastic - there's no way I can tell when the fluid is getting near the top.

I can't imagine that when you fill, you have to fill until it starts backing up out the top of the fill tube.

And for those that say "just put in X gallons when you get the nth warning", what if your sensor is not working properly? How do you know how much you really have in the tank?

My DIC said I was at 30% for about a day. Then it said it was fine for a few days. Then it said I was at 30% for a couple days. Now it says it's fine again.

So... am I at 30% full or do I have a malfunctioning sensor?

Thanks for any insights.

[Javi]

Look folks...

DEF isn't a magic solution... It is a fertilizer

I've literally made millions of tons of the stuff... it is a solution of a solid (UREA 46-0-0) in water to produce a 32.5% solution.

Remember from high school chemistry that temperature, percentage of solids to liquid and agitation or among the controls of a solid remaining in a solution.

Pouring NEW DEF into OLD will not hurt anything unless the solution has lost some of the liquid; possibly through evaporation. But even that will help by increasing the percentage of liquid to solid. DEF or 32.5% UREA will freeze and the solids will begin to FALL OUT as it approaches 12`F and if warmed the solids will return to solution with agitation (driving) to the percentage allowed by the controlling temperature.

This is why there are heaters in the tanks... with the exception possibly rupturing the tank from expansion there is no harm to the DEF freezing as long as it is brought to a reasonable temperature and agitated by driving..


My only cautionary advice in the use of DEF is to thoroughly wash any metal or painted surface that it spills on... it will promote oxidation (big time) :D

Oh..... it is colorless until color is added... Mississippi Chemical Company used to ship a 5 gallon bucket of color for us to add to their product which they called GOLDEN 5 gallons of powder to 1,000,000 gallons of solution...

32.5-0-0 is 32.5-0-0 is 32.5-0-0 no matter who makes it... water quality (purity) would be the only variable...

[Javi]

How are you supposed to know how much to put in? Assuming I want to fill it, I know that the tank takes 7 gallons, but I don't know how much is still in there. I just looked at the DEF fill tube and it is black plastic - there's no way I can tell when the fluid is getting near the top.

I can't imagine that when you fill, you have to fill until it starts backing up out the top of the fill tube.

And for those that say "just put in X gallons when you get the nth warning", what if your sensor is not working properly? How do you know how much you really have in the tank?

My DIC said I was at 30% for about a day. Then it said it was fine for a few days. Then it said I was at 30% for a couple days. Now it says it's fine again.

So... am I at 30% full or do I have a malfunctioning sensor?

Thanks for any insights.

Just like your fuel tank... pour it in until it gurgles or burps... put the cap back on and rinse any spillage off the surrounding metal and painted surfaces..

[mikec557]

Just like your fuel tank... pour it in until it gurgles or burps... put the cap back on and rinse any spillage off the surrounding metal and painted surfaces..

That's easier said, than done. On my '18 GMC the fill tube on the firewall is surrounded by a small box maybe 3x3 inch and a half inch tall. That's the entire overfill catch basin. The DEF/jug fill tube is the exact size dia. of the fill hole, such that no air can enter or exit the fill hole. The fill tube that comes with the DEF is an easy inch in diameter, probably more, and about 16 inches long. When you tip the jug up you get a solid column of liquid. If the tank and tank fill tube becomes full, then the jug's fill tube is also full right back up into the jug. There's no way to remove the jug fill tube without spilling most of its contents all over the firewall and everything on it.

Given that, I think it's easier to add either a 2.5 gal jug, or drive a little further so you can safely add two of the 2.5 gallon jugs. But it is a guessing game. And with all the technology we have, it shouldn't be.

Just my 2 cents
Mike

[Javi]

That's easier said, than done. On my '18 GMC the fill tube on the firewall is surrounded by a small box maybe 3x3 inch and a half inch tall. That's the entire overfill catch basin. The DEF/jug fill tube is the exact size dia. of the fill hole, such that no air can enter or exit the fill hole. The fill tube that comes with the DEF is an easy inch in diameter, probably more, and about 16 inches long. When you tip the jug up you get a solid column of liquid. If the tank and tank fill tube becomes full, then the jug's fill tube is also full right back up into the jug. There's no way to remove the jug fill tube without spilling most of its contents all over the firewall and everything on it.



Given that, I think it's easier to add either a 2.5 gal jug, or drive a little further so you can safely add two of the 2.5 gallon jugs. But it is a guessing game. And with all the technology we have, it shouldn't be.



Just my 2 cents

Mike1. I'm sorry that GM put the full tube in an inaccessible location.

2. I've never put more than or less than two and a half gallons in my tank at any point since the inception of the system.

3. Ford actually sells a fill tube with a burp vent, wonder if GM might have the same available.

[C130JSuperHerc]

In have a 2016 and never had an issue.

It says def ok until 40%. I think it starts giving you mileage alerts less than 30

I usually add a 5 gallon jug once per oil change (~7K miles).

Only once did I top it off and it was stuck at 40...it cleared up after a few days of driving...sensors are probably like the ones in your black tank...if you get build up on them it take a while to get it off.

[roadglide]

I know the L5p uses a lot more Def then my MIL. The inside gage is suppose to be improved over the LML.i was told at 30% add 5 gallons I haven't
been there. I have though about trying that . I came up with a sheet metal and wood inside support I made . The plastic top from inside a old ice chest perfect fit for 5 gallons of DEF. There easy to fill from any truck stop. Def will last 2 years mild weather from Google search high tempture is much worse then freezing.

[roadglide]

I know the L5p uses a lot more Def then my MIL. The inside gage is suppose to be improved over the LML.i was told at 30% add 5 gallons I haven't
been there. I have though about trying that . I came up with a sheet metal and wood inside support I made . The plastic top from inside a old ice chest perfect fit for 5 gallons of DEF. There easy to fill from any truck stop. Def will last 2 years mild weather from Google search high tempture is much worse then freezing.I have been hauling 5 gallons of Def attached containment at the back of my Anderson hitch . I had filled the Def befor leaving on my Az trip 3900 miles later I get message low Def fluid 30%. I added 4 1/2 gallons to fill the 7 1/2 gallon tank. That's averaging 866 miles gallon . 2000 was towing heavy .

[travelin texans]

The spout on the jugs have a small rubber vent tube in them, while filling if you want to stop the flow simply place your finger over the tube, all you may lose is what's in the spout if you pull out to quickly, put the plug back in & rinse off what spilled with a water hose.

[roadglide]

I like the duramax fill system the container lays down under the hood as I start tilting the jug insert the tube in and fill it by gravity it will stop when full . The same principle as gravity feed fuel transfer tank, if the jug is lifted and try forcing more fluid from the continue it flow out into the over flow funnel onto the ground through a hose .