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Old 01-13-2019, 07:48 AM   #1
MarkEHansen
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Unreliable DEF tank monitor in our GMC Sierra 3500 HD?

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,
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Old 01-13-2019, 07:53 AM   #2
jimthemosaicguy
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Unreliable DEF tank monitor in our GMC Sierra 3500 HD?

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.
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Old 01-13-2019, 03:25 PM   #3
mikec557
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Quote:
Originally Posted by MarkEHansen View Post
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
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Old 01-13-2019, 03:33 PM   #4
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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....
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Old 01-13-2019, 03:49 PM   #5
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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.
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Old 01-13-2019, 04:02 PM   #6
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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.
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Old 01-13-2019, 04:03 PM   #7
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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,
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Old 01-13-2019, 04:09 PM   #8
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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.
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Old 01-13-2019, 04:29 PM   #9
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...
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.
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Old 01-13-2019, 04:33 PM   #10
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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.
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Old 01-13-2019, 04:34 PM   #11
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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...
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Old 01-13-2019, 04:40 PM   #12
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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..
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Old 01-13-2019, 04:49 PM   #13
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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.
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Old 01-13-2019, 05:04 PM   #14
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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
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Old 01-13-2019, 05:36 PM   #15
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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
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Old 01-13-2019, 06:14 PM   #16
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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?
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Old 01-13-2019, 06:27 PM   #17
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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.
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Old 01-13-2019, 07:13 PM   #18
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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.
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Old 01-13-2019, 09:23 PM   #19
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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.
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Old 01-14-2019, 07:52 AM   #20
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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" ????
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