DEF Fluid Warning

[Camper0414]

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.

[D2Reid]

Welcome to the forum. If it were me I would take pictures of the dash and record the mileage and type of driving then take it to a dealer, sounds like a control module problem what should be covered under warranty.

[That 1 Ron]

Welcome to the forum. If it were me I would take pictures of the dash and record the mileage and type of driving then take it to a dealer, sounds like a control module problem what should be covered under warranty.

I agree with this. Take pictures of messages on the dash and find a gm dealership/service center. My guess is either a sensor or wiring harness issue but it just might need a re-flash. My father-in-law just went through something similar on his 2019 D-max which turned out to be a sensor in the DEF tank.

[BreakfastinAmerica]

FYI

DEF and mpg should be fairly equal. I get @4000 miles w/o towing at 19mpg. When towing I get 10mpg and @2000 miles on DEF.

[traveldawg]

Ford guy here..... When not towing it seems I use less DEF than when towing. No scientific proof or logging. But it seems that way.

And, not that DEF is involved, but the regens come at shorter distance intervals when towing. When not towing it seems pretty consistent at about 497 miles (and the percent soot gauge shows 100% too) and the region brings the soot level down to about 12%.

When towing it might be 300 miles or so when a regen occurs and also when the soot gauge shows 100%. But it only burns down to about 27%. I'm trying to figure out if the regen burn is a timed event or if it senses soot levels.

So I figure if regens are more frequent when towing that I must be sooting up soon which means something is working harder and maybe using more DEF.

[CoChris]

I'm trying to figure out if the regen burn is a timed event or if it senses soot levels.

So I figure if regens are more frequent when towing that I must be sooting up soon which means something is working harder and maybe using more DEF.

Both, a regen is triggered by either the soot level (measured as pressure differential across the DPF - Diesel Particulate Filter (a ceramic disk with many very small holes through it)) exceeding a threshold or roughly 500 miles. Whichever comes first. Oh, and certain engine parameters have to be met (engine warmed up, minimum speed, etc) to start the regen.

In the current Fords (I do not know about other brands, but probably applies) there are two types of "regen" passive and active. Passive happens under heavy loads (and normal driving?) when the exhaust temp is high enough to burn off the soot. This typically does not reduce the soot load, but rather slows down the accumulation of soot. The higher and longer the load (i.e. towing ) the more effective this is. The other type is what we all know and love (insert your favorite emoji here), and is called active regeneration. This is where they dump raw (unburned) fuel into the exhaust pipe and it burns in the pipe down stream of the engine greatly increasing the temperature at the DPF and thus burning the soot/oil into a fine ash.

Towing is a balancing act between burring more fuel and thus generating more soot and running at a higher exhaust temperature thus burning off or at least slowing the accumulation of soot in the DPF.

DEF (Diesel Exhaust Fluid) is also an emission control approach but it is aimed at reducing NOx (Nitrous Oxide) emissions, this is completely separate from soot. However, they are both effected by engine temperature (i.e. how heavy of a load). Higher temp/load tends to reduce the soot but increase the NOx emissions. I notice I get longer time between regens, but use much more (3x~4x) DEF when towing compared to unloaded driving. That is just my experience.

Hope that helps some

Chris

[Wynn1427]

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.

The 600/360 number yours shows doesn't seem to be too far off what may be real world numbers of not towing/towing (see below), also YMMV based on how hard it is pulling during trip. Have a friend who has '05 gm and pulling through mountains I look back and see the black smoke coming from his exhaust on numerous occasions (not from ours due to def fluid requirement on newer vehicles), harder pull will use more def.

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/

[el Rojo]

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

[Redapple63]

My GMC is woefully inadequate as it relates to DEF remaining. I have found the reporting to be unreliable. I have only gotten the DEF message twice, first time a month after purchase. Clearly the dealer did not add any. Put 6 gals in a 7 gallon tank.

2nd time was this past December on my way home from a San Diego camping trip. It is only 130 miles from my house. About halfway home I got the DEF warning with 1000 miles message. By the time I got home it was down to 100 miles. All within the span of about 65 miles actually driven.

To me that message equates to put DEF in as soon as possible.

Thanks,
Bill


Sent from my iPhone using Tapatalk

[WhittleBurner]

My GMC is woefully inadequate as it relates to DEF remaining. I have found the reporting to be unreliable. I have only gotten the DEF message twice, first time a month after purchase. Clearly the dealer did not add any. Put 6 gals in a 7 gallon tank.

2nd time was this past December on my way home from a San Diego camping trip. It is only 130 miles from my house. About halfway home I got the DEF warning with 1000 miles message. By the time I got home it was down to 100 miles. All within the span of about 65 miles actually driven.

To me that message equates to put DEF in as soon as possible.

Thanks,
Bill


Sent from my iPhone using Tapatalk

Our GMC is the same way. Seems like if you are towing or hit a hill, anything that makes you use more power The mileage the to go reduces quite rapidly. When that warning comes on we start looking for a place to get more DEF as soon as possible.