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Excessive DEF consumption, 2019 Denali Duramax

33K views 81 replies 27 participants last post by  redwngr 
#1 ·
I have just over 13,000 miles on my 2019 GMC Sierra Denali Duramax now, all has been OK until this trip. My fuel mileage had been increasing, etc. as the miles went on. This trip, my DEF usage has gone to 7 gallons every 1500+ miles, fuel mileage has dropped to 9 mpg (it had been over 12 towing), I don't get the usual DEF notifications. No 30% or 1000 mile notification, just an Action Required Now-engine will shut down in 500 miles. The power seems to be OK. I have taken it to a shop on this trip, they checked the system for leaks and said they make some ECM updates--it didn't change anything. I have a GM reference number now so I'll be taking it in when I get home. Just wondering if anyone has any info I can help the dealer with. Thanks.
 
#2 ·
Did you fill the DEF tank before you left? I ended up adding 7 gallons on my new truck on a trip over the first 1500 miles but clearly it was only at the minimum levels when I picked it up new. Since then it has settled into expected usage. If it were mine, I would just keep driving it until the warning comes on. Keep a 2.5 gallon DEF container in the truck just in case.
 
#8 ·
Expected DEF Usage



Yes, mine was at minimum level when I picked it up. However, since then, I've been recording DEF usage. I do carry DEF with me at all times, since if I put 2.5 gallons in, in 600 miles it's telling me Action Required add DEF. I don't think my expected usage should be 2.5 gallons every 600 miles, it should be more like 2500 miles every 2.5 gallons. My 2016 Chevy Duramax went over 5000 miles on 5 gallons.
 
#3 ·
Nutdriver,

Not sure about everyone else but I've done some extensive calculations since I got my truck and figured out that my DEF was being used at a rate of about 777 mi/gal of DEF. Was fun when I went to the dealer after they did my first maintenance and I had to school them on the calculations I did: I asked before they performed the maintenance if they were going to top off my DEF tank since it was at 14% when I brought it in and they said yes, only to discover that a week later it was reading low... I ended up going back to ask them how this was possible and they tried to tell me there might be a leak- I told them I had already checked myself and there was no leak or cracks or anything I could see but that they were welcome to check it but I was pretty sure they didn't fill it. After a lot of back and forth the manager came out and tried to BS me that they had filled up my DEF tank. He was really surprised when I showed him my calculations on this as well and that my numbers showed they must've only put 1 gallon, just enough to indicate the level was "OK", or else something was seriously wrong with the truck and that being the case I wanted them to figure it out and prove it to me. At that point he had no choice but to admit they must've only put 1 gallon, not topped it off. I asked if that was standard practice and he beat around the bush and ultimately said yes, they just put enough to get rid of the percentage warning which I think is ridiculous because if they're supposed to top off fluids at a maintenance interval, this should be included IMO. Anyhow, my calculations have been spot on so far with the 777 mi/gal estimate. I'm sure driving habits can make that differ but that's how mine has been.

On a side note, couldn't help but notice your TDIs in your signature. I had a 2014 VW Jetta Sportwagen TDI. Opted for the buyback and turned her in Nov. 2018 and upgraded to my truck. Got $28,300 from VW for my wagon with over 65k mi. on it. Miss that wagon, was getting 40-55 mpg with it. Enjoy your TDI.
 
#4 ·
Wonderwoman - I have not tried to be that precise in part because my DEF tank was clearly not full when I picked up my truck new. I am trying to not fill the DEF tank until I get the first 30% warning and noting the miles driven at that point. I am trying to then fill the tank and drive until I get another 30% warning. I would then know roughly how many miles I am getting per refill. My use seems to be within expected levels.

When I had my vehicle serviced for one of the free oil change services, I had asked before the visit and they indicated that they would add 1 gallon to my DEF. I am not sure in hindsight that was done since it was not listed on my service record.

The VW TDI Jetta has been a great daily driver. I have 280,000 miles on it currently. Prior to this 2006 VW, I had a 2000 TDI with 160,000 miles totaled by a deer hit. Both have been reliable cars and the 41-45 mpg has been great. Not unusual to see 60+ mpg when driving with a decent tailwind.
 
#7 ·
I knew how much the dealer I purchased from had in it when I took it off the lot so I’ve been able to do my calculations the whole time which is how I got that number. I’m sure driving habits probably have a play in it too but in my case I have the same route every day. It’s my daily driver. I definitely get the over 5k miles from a full tank of DEF 🙂

Man... It was so hard for me to part with my wagon. I knew I would probably regret doing the buyback but the money they offered was too insane not to do it. Before the TDI scandal, my intention was to drive it til it fell apart and I figured I could get close to 500k miles from it. I sure miss it but if the truck treats me well, it’ll have been a good move.
 
#9 ·
Similar Problem

I also have a 2019 Denali 3500HD, and have also been seeing very high DEF usage. It used over 12 gallons of DEF in the last 2400 miles. 2200 of the miles were towing a boat (~10,000 lbs). I also am not getting any warnings. It goes from "OK" to speed will be reduced to 65 in x miles. I had to put 2.5 gallons in every 400 miles not he return trip home. Also no leaks in the system and no drop in power or performance. Please update this post if you get it fixed.
 
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#10 ·
OK, here's my calculations: '18 High Country Dually, 98% of mileage of just over 15K pulling heavy approx 19.5K pounds.
I wait until I get the 30% DEF warning and at that point I can dump in 5 Gal of DEF. Just did the cal and I'm burning
a Gallon of DEF every 471 miles, that's a lot more than my '11 LML did pulling the same weight.
 
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#13 ·
OK, here's my calculations: '18 High Country Dually, 98% of mileage of just over 15K pulling heavy approx 19.5K pounds.

I wait until I get the 30% DEF warning and at that point I can dump in 5 Gal of DEF. Just did the cal and I'm burning

a Gallon of DEF every 471 miles, that's a lot more than my '11 LML did pulling the same weight.


That would probably be about right. How many gallons of diesel did you burn over the same time. Def usage is usually 1-2 % of diesel usage.

One guy on another forum said the def could be diluted to about 66% of normal def and it would still work fine. That would be 2 gallons of def and a gallon of distilled water. But I wouldn’t do this in a real cold climate.
 
#11 ·
GM has issues with the DEF gauge readout. I know mine is a 2020 BUT it happens on the earlier 18 and 19's as well. Mine jumps around even when it is almost full shows half or on a recent trip gave me the warning of xxxxx miles until empty. It took 1.4 gallons to fill it to the top when showing almost empty. After filling went to half then 2 days later went to full.

Point is it is not accurate and I carry DEF all of the time. Gave GM the notification letter (Dealer got a copy as well) per the instructions, call to them verified and have a case number now. Pursuing this Dealer under the Vernon Articles (Texas LL). The software was flashed on the 1st attempt did nothing and waiting for the strike to be over and the repair backlog at my dealer which is one of the biggest ones GM has because of parts non availability. This will be the 2nd attempt out of 3 and the Dealer is working with GM to determine what the next repair attempt will entail.

Do not want to be in the middle of nowhere and the truck decide it is out of DEF and goes into limp mode. Will just let them replace it if they cannot fix it.
 
#18 ·
I haven't calculated how much Fuel I've used but I've had my 2019 since August 6, 2019 I just rolled over 4900 miles and I've put 4 x 2.5 (10 gallons) of DEF in it so far. They swore it was full when I left the lot but based on some of your comments it probably wasn't. Of that 4900 miles I did 1300 miles pulling my 38' 10K lb travel trailer and got a whopping 7 miles per gallon doing it. I hear wait for the break in but I traded my 2018 w/48K miles on it for this 2019 (long story) and it never got better than 7-8mpg pulling. Anyway, I know this is about DEF but seems based on some of your calculations for 10 gallons of DEF I should have gone 7000 miles. I'd say I'm using a lot. I used a ton on that 1300 mile trip as I had to stop about 800 miles in and add 5 gallons. Thank God I found a 24 hour Wal-Mart in the middle of no where cause I was stupid and started the trip without a spare bottle. It went from you have 999 miles to go to you are about to have problems in about 30 miles. It seems to be using quite a bit. I'll be keeping an eye on this and this post to see what you guys come up with.
 
#63 ·
That's the same one posted a few post down about the computer not throwing a cel in the case you do have excessive regens.
 
#20 ·
I have searched for your excessive regen recall and do not get a single hit. What year vehicle do you have? Can you provide any more info??

Thanks
 
#22 ·
Thank you for the reply.

I searched the net, and also went to gm site and entered the vin and only have the heater cord listed. Mine is a 2019 (10/19 mfg date)

Maybe its a canada thing, or maybe they will post mine in a few days.

If you get it done, would sure like to hear back if it helps regen interval.

Regards,
 
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#25 ·
I've got a similar issue. I bought a 2020 3500 last Saturday. I've got 270 miles on it now and I've lost 2 bars on my Def tank gauge (so I'm down a quarter tank). If the tank was full when I left the dealership, and I'm hoping it wasn't, I'm on track to use 5 gals of Def fluid in 1,000 miles!!?? This has been around town driving, nothing being towed.
 
#26 ·
I think that for those with a new vehicle, the first thing to do is to confirm that your def tank is full. Then keep good notes as to how many miles you are driving and how much def you need to add. The driving conditions also are important. More fuel used when towing will also consume more DEF.
 
#30 ·
My 2019 2500HD with a known full DEF tank from dealer got 3750 miles before any warnings, this was with a combo pulling 4000 lbs TT and daily driving.
I'm now at 5100 miles and have not be able to add more then about 1.5 gallons in that time and no towing. I've been topping it off, perhaps I will stop and let it run down again to get a second calculation.
 
#31 ·
2019 with 9700 miles, 20% towing 8k lbs. I topped off at 500 miles to establish baseline. Filled twice since then and running 740 miles/gallon, and 1.7% of fuel IIRC.

You might want to rethink frequent topping off. DEF has a 2 year life, so you want to add at the lowest possible tank level to minimize the older material still in the tank that mixes with the new. Pretty sure my owners manual even warns against frequent topping off.
 
#32 ·
You might want to rethink frequent topping off. DEF has a 2 year life, so you want to add at the lowest possible tank level to minimize the older material still in the tank that mixes with the new. Pretty sure my owners manual even warns against frequent topping off.
I follow this strategy as well. I wait until my DEF warning comes on then either fill with one 2.5 gallon container or 2 depending on how much driving I anticipate doing.
 
#33 ·
I always wait at least til the 1000 mile warning.
This seems to come somewhere between 18% and 23% on this truck.

I have also taken it all the way to the 'def tank empty' message, just to be able to say I did -- and to see what the 'xxxmiles to 65mph speed limit' message would look like :)
 
#34 ·
def tank empty' message,500 miles to 65mph speed limit' message is all I have ever seen since new at 18,000 miles , no warning in advance of that and most it has ever taken is 5.8 gallons. 3 dealers say thats the way it works, I call BS but does no good.
 
#35 · (Edited)
You are correct.

Should also get a one time message that exhaust fluid range is down to 1000 miles.
(when my '18 gives this message, the DEF indicator will be somewhere between 18 and 22%)
At 300 miles or less, it should give another range remaining message, and below 300 miles it should repeat the message each time it is started. (which of course might be never, if on a road trip)
The above messages are all 'clearable'.

When it gets to 'empty' the 500 miles til speedlimit countdown display takes over the DIC.
When I tested this there did not seem (I couldn't find?) anyway to clear the message.
As soon as I filled the tank the message cleared.


(Yes, getting to the 'empty' level was intentional, just to see what the message looked like >:))


Owners manual (diesel supplement) has all the messages listed.
They did a lousy job of adding the info for the 2.8L diesel.
 
#36 ·
When it gets to 'empty' the 500 miles til speedlimit countdown display takes over the DIC.
When I tested this there did not seem (I couldn't find?) anyway to clear the message.
As soon as I filled the tank the message cleared.

Very annoying when it takes over and the DIC becomes useless. I am going to try my local dealer and see what they say and then I guess call GM and start a complaint, the "500" miles take about 200 to to count down, just waiting for the day it goes straight to reduced speed?
 
#38 ·
Mine was, and is, working exactly as the 'book' says it is supposed too.
The countdown thing certainly annoys as it is intended too.

Still have all the dash gauges when this is going on so missing the extra stuff available on DIC isn't critical.


I normally wouldn't run it to empty, but curiosity got the best off me -- so it was intentional.

My post (that you quoted) was only intended to provide info about what might be expected. I'm certainly not trying to suggest that running to empty should be standard practice.

IMO the truck provided lots and lots of warning.
 
#39 ·
I want to give you the latest update regarding my excessive DEF usage issue. I took my truck 2 1/2 hours away to the selling dealer. Within 2 hours, they had diagnosed the DEF nozzle injecting over double the specified DEF into the system. Two days later, they had the parts installed, the rest of the system tested and other service work done that was due. Now I'm driving to test the usage, which might take a while with all the "stay at home" in progress, and since I don't drive this truck much except when we travel. 22799 miles on truck now.
 
#41 ·
So I posted on here 8 mos ago when I towed my 10K travel trailer from Arkansas to Arizona and used a full tank of Def in 800 miles. I just travelled back from there and at 846 miles my DIC went from OK to you will be limited to 65 mph. (never have gotten that message before). I had topped off the tank before I left on the trip and I put 5 gallons in. So I know I used at least 5 gallons of DEF maybe more in 846 miles. This is my 4th Duramax starting with my 2012 Denali HD and this one by far uses the most fuel and def. Of course I've had it to two dealers and you can tell they are trained by the same group..."You didn't buy this truck for it's fuel mileage did you" I really miss my 2015 LML I got 10 -12 pulling my camper driving the same way I always do (usually speed limit to 5 over with cruise set). This last trip I averaged 6 mpg.
 
#43 ·
So I posted on here 8 mos ago when I towed my 10K travel trailer from Arkansas to Arizona and used a full tank of Def in 800 miles. I just travelled back from there and at 846 miles my DIC went from OK to you will be limited to 65 mph. (never have gotten that message before). I had topped off the tank before I left on the trip and I put 5 gallons in. So I know I used at least 5 gallons of DEF maybe more in 846 miles. This is my 4th Duramax starting with my 2012 Denali HD and this one by far uses the most fuel and def. Of course I've had it to two dealers and you can tell they are trained by the same group..."You didn't buy this truck for it's fuel mileage did you" I really miss my 2015 LML I got 10 -12 pulling my camper driving the same way I always do (usually speed limit to 5 over with cruise set). This last trip I averaged 6 mpg.
6 MPG pulling a 10,000 lb camper? Bucking a wind or pulling in mountains or both? Wow never got 6 MPG with any diesel pulling trailers ever and i pulled some big heavy trailers back in the day, in the wind and up in the mountains. I don't ever let it go into overdrive though i do the manual shifting thing and keep it out of Overdrive.
6 MPG is insane! I got 8 MPG once when a computer or something went goofy and they had to replace it. Then back to 12-16 MPG. This is with Ford and Chevy diesels pulling trailers.
 
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