DEF guzzling during towing

[Graphics1988]

So.....my 2023 LT Trail Boss Duramax...........it is a miser on DEF when I am doing the daily driving....BUT...tow anything and it inhales the stuff! ...which then lead me to a suspicion about the trailer plug in. (stay with me here)....i had this brain fart, that MAYBE when you plug in the trailer harness, it tells the computer to chug the DEF (without caring about 'what' trailer weight etc is)...so MAAAAAAYBE, the trailer harness completes a 'computer loop' to pump the extra DEF dosage.

Here's where it gets interesting ---- I tell this to my buddy who has the same truck (except Denali), he looks confused and says...'nahhhh...he then says OK, I will plug in my trailer harness (no trailer) and drive home tonight'.

Welp --- his fuel economy gets worse by a LOT and his truck starts pumpin the juice - goes in regen etc and he is now convinced, the trailer harness plug is a trigger for all things bad about this towing issue that many are having.

Anyone else do a test like this? ...maybe there's a few dozen threads already about this --- I havent looked -- sorry if so.

 

[as73]

I have the 2022 model, I just towed a 7k trailer 400mile and still averaged 17 mpg. No change in DEF consumption noticed. However I will keep an eye on it. I let my truck idle for extended periods of time(Dogs in truck) and it almost always goes in Regen. You can tell by a notable engine/exhaust tone change.

 

[Graphics1988]

I have the 2022 model, I just towed a 7k trailer 400mile and still averaged 17 mpg. No change in DEF consumption noticed. However I will keep an eye on it. I let my truck idle for extended periods of time(Dogs in truck) and it almost always goes in Regen. You can tell by a notable engine/exhaust tone change.

Ya that's great! I would be happy if mine was like that - I ended up around 13mpg pulling my enclosed sled trailer(around same weight as you were pulling) and drinkin the kool-aid like crazy ..maybe I will see if the dealer can tweak it...cheers

 

[BigJake]

Ya that's great! I would be happy if mine was like that - I ended up around 13mpg pulling my enclosed sled trailer(around same weight as you were pulling) and drinkin the kool-aid like crazy ..maybe I will see if the dealer can tweak it...cheers

my 2023 drinks the def like crazy when towing, so much it has thrown my gauge off, it will say fill def soon as it’s overflowing out of the tank and my banks idash even says def tank is 98% full, I towed a 27’ trailer from Louisiana to utah and had to stop several times to add def along the way. Hopefully my gauge recalibrates soon as I have read another person had the same problem.
When I am empty, I rarely have to add any.