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]

Originally Posted by 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,

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]

Originally Posted by 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....

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,

[mikec557]

Originally Posted by MarkEHansen

...
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.

[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]

Originally Posted by 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.

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.

[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.

[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]

Originally Posted by 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...

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..

[PARAPTOR]

Originally Posted by Javi

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

[mikec557]

Originally Posted by 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...

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.

[tundrwd]

Originally Posted by 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...

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/a1...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!

[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

[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.