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-MGRV]

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/topic/243679-def-usage-on-2020-hd-models/#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.

 

[Fivecodys]

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/topic/243679-def-usage-on-2020-hd-models/#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,

 

[Wynn1427]

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.

 

[JTP303]

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?

 

[Fivecodys]

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.

View attachment 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.

 

[Canadiansteelman]

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.

 

[Beach Commander]

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

 

[JessJoe4168]

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

 

[KB5SET]

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!

 

[curt48044]

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.

 

[cfowler55]

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