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  1. #11
    Seasoned Camper Fivecodys's Avatar
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    Quote Originally Posted by Wynn1427 View Post
    Have some numbers as we just got back from 1200mi trip with our setup, from Central Cal through Tehachapi (CA) and I40 (CA/AZ) to Grand Canyon (lots of varying grades throughout the trip) and averaged 10mpg running 60-65mph. Dumped 2.5gal before leaving each way, so used 5gal total of DEF fluid on our trip. Swear both times I saw the same 1000mi message, checked and def level was at the 3/4 full mark also, both messages occurred on a downgrade (not sure if coasting down compared to climbing through elevation throws computer system for a loop or just coincidence). For some reason mine doesn't show remaining mileage for def tank on that screen, just shows the green bar display. 1200mi / 5 gal ~ 240mi/gal def. None towing estimate (taking ownership of truck last Sep) 5900 mi / 7.5 gal ~790mi/gal def. Seems to be in line with few posts of the gm thread - https://www.gm-trucks.com/forums/top...dels/#comments. Seeing my numbers now, I will fill up before trip and carry additional along the way. Also use this link before dumping def fluid in tank for mfr. date/shelf life - https://thecampingadvisor.com/blue-def-date-code/
    I have a 2019 and I am curious how you are checking the DEF level. All I have is the gauge on the dash display that tells me I'm "OK" or prompts me that I'm getting low.
    Can you elaborate a little on your process please?

    Thanks,
    2020 Reflection 29RS 5th Wheel
    2019 GMC 2500 HD 4x4 Duramax

  2. #12
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    Quote Originally Posted by Fivecodys View Post
    I have a 2019 and I am curious how you are checking the DEF level. All I have is the gauge on the dash display that tells me I'm "OK" or prompts me that I'm getting low.
    Can you elaborate a little on your process please?

    Thanks,
    2020 has option to display DEF gauge in the info tab of DIC, believe option to display gauge was within the DIC menu settings. Manual has table which give approximate gallons to fill and been using that as my estimate to usage. Notice the table/approx. DEF is not linear relation to bars gone so using mid-point as common position seems best in the estimates, could be more accurate if one was to fill DEF fliuid at a station. I dump 2.5gal in when mine shows half gauge and it goes to full. I was able to figure out how many times I have bought DEF fluid in the last 7 months, truck keeps track of mileage towing trailer, total non-towing miles is total miles - trailer miles it tracks. 2020 manual indicates a 7gal total DEF fluid tank, leaving ~2.5gal for last gauge bar/empty sliver. Guessing it is non-linear so people don't run it down everytime and truck goes into limp mode.

    Click image for larger version. 

Name:	Def Table.PNG 
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ID:	33247
    2020 GMC 3500 Denali SRW SB Duramax 4x4
    2021 Reflection 31MB Goosebox 16k

  3. #13
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    Quote Originally Posted by Camper0414 View Post
    We are towing our Grand Design 5th wheel with a 2020 Chevy Silverado 2500 Heavy Duty Diesel and we received a DEF Fluid warning for 1000 miles. When we check the level it is at 3/4 full. The mileage does not seem correct because over the winter we would fill up with DEF Fluid and it would say 600 - now that we are towing we fill up with DEF fluid it says 360. We are thinking it is because we use more DEF fluid when towing so it throws the formula off and gives a warning. BUT if the truck is going to regulate speed because of thinks it is low we are out of luck. How do we move forward, the truck thinks it is low. The fluid is in there. The system is going to take over. It’s like the brain doesn’t the bladder if full.
    I have seen similar information from my truck. In researching I discovered that GM has identified the issue and issued a software update to resolve it. The update is covered under warranty. Have you had it updated yet?
    Jeff and Gale
    Vancouver, WA
    New - 2020 GMC 3500 Duramax
    Old - 2005 GMC 2500 Duramax
    New - 2021 Solitude 310GK
    Old - 2018 Reflections 303 RLS

  4. #14
    Seasoned Camper Fivecodys's Avatar
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    Quote Originally Posted by Wynn1427 View Post
    2020 has option to display DEF gauge in the info tab of DIC, believe option to display gauge was within the DIC menu settings. Manual has table which give approximate gallons to fill and been using that as my estimate to usage. Notice the table/approx. DEF is not linear relation to bars gone so using mid-point as common position seems best in the estimates, could be more accurate if one was to fill DEF fliuid at a station. I dump 2.5gal in when mine shows half gauge and it goes to full. I was able to figure out how many times I have bought DEF fluid in the last 7 months, truck keeps track of mileage towing trailer, total non-towing miles is total miles - trailer miles it tracks. 2020 manual indicates a 7gal total DEF fluid tank, leaving ~2.5gal for last gauge bar/empty sliver. Guessing it is non-linear so people don't run it down everytime and truck goes into limp mode.

    Click image for larger version. 

Name:	Def Table.PNG 
Views:	22 
Size:	45.5 KB 
ID:	33247
    That's really cool. I just get the 1,000 mile warning and then a 500 mile warning. Thanks for responding though, I appreciate it.
    2020 Reflection 29RS 5th Wheel
    2019 GMC 2500 HD 4x4 Duramax

  5. #15
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    Quote Originally Posted by Camper0414 View Post
    We are towing our Grand Design 5th wheel with a 2020 Chevy Silverado 2500 Heavy Duty Diesel and we received a DEF Fluid warning for 1000 miles. When we check the level it is at 3/4 full. The mileage does not seem correct because over the winter we would fill up with DEF Fluid and it would say 600 - now that we are towing we fill up with DEF fluid it says 360. We are thinking it is because we use more DEF fluid when towing so it throws the formula off and gives a warning. BUT if the truck is going to regulate speed because of thinks it is low we are out of luck. How do we move forward, the truck thinks it is low. The fluid is in there. The system is going to take over. It’s like the brain doesn’t the bladder if full.
    Did you try resetting the trip meters when pulling the trailer. This may help the computer recalculate remaining DEF miles more accurately.
    2018 Reflection 303RLS, PullRite 16K Superglide, 2022 GMC 2500HD Duramax Denali.

  6. #16
    Left The Driveway
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    I'm just thankful that my d e f gauges and warning system quit working miles and miles ago so I can run it all the way empty and don't get any warnings and nothing shuts down . 2011 GMC HD Duramax I have 93,000 on the truck the d e f warning system quit working around 30,000

  7. #17
    Fireside Member JessJoe4168's Avatar
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    The DEF usage can usually be estimated by relating it to the fuel burn.
    Maybe it is 1-2% of DEF per gallon of fuel
    JessJoe - Eastern PA
    2019 Reflection 29RS - Reese GooseBox
    2017 Ram 2500 6.7L 4x4 SRW SB

  8. #18
    Setting Up Camp
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    I have the same setup, Chevy 3\4 2020 Duramax.
    I have noticed the exact same thing on my truck.
    I have run the DEF down to 2 bars with no issues.(I did get random messages)
    Somewhere I read you should refill when it gets down to 2-3 bars, just in case.
    Like you, my truck uses about 4 times as much DEF when towing.
    Dealer says that this is normal.
    At least we don't have to fill the DEF tank under the hood near the firewall.
    Now the refill is in the fuel tank opening.

    Good luck!

  9. #19
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    Take photos of the message, your DEF level and your MPG average and take it to the dealer. There have been 2 software updates I believe for MY20 in regards to the DEF level and usage parameters. My guess is that you have not gotten at least one of the updates.

  10. #20
    Rolling Along cfowler55's Avatar
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    Quote Originally Posted by el Rojo View Post
    Our 2015 Chevy would warn us at about 800 miles left, then around 500. When the low def light light came on I would add 2.5 gals (20% left in the tank). Never had it shut me down. I did have to get the sensor replaced in the DEF tank (under warranty) though.

    Now my 2019 Ram drinks def. I don't get much more than 1000 miles out of 2.5 gal of def when towing (2000 not towing). Fuel mileage is usually 8 mpg. But this truck is a beast. It has the H/O engine with 4:10 rear gears. No comparison in power to the Duramax with 3:73 rear end and about the same mpg, but double the def consumption. I guess you have to pay for power.

    Red
    This makes me feel sooo much better. I thought I was the only RAM owner out here getting less than 12-15 towing. Two HO RAMs , +30k miles towing. Long term average 8.2 mpg. I have seen upper 9’s , but also mid 6’s. DEF usage averages one gallon to 50 gallons of diesel , or within a few miles of 400 per.
    Charlie
    Vickie & Charlie
    2019 310GK-R
    2020 RAM Longhorn DRW Cummins /Aisin

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