Def usage - seemed to drop really fast

[drmoose]

So I was on a drive last night, some winter/mountain driving, 370mi one way, temps around/below 30 most of the time. Speed between 65-74.

About 60 miles into the drive, I got a 995mi DEF warning. I had about 300 miles to go, thought it shouldn't be a problem. I checked, there were 3 bars left on the gauge. Then about ~90 min later I got a Low DEF warning, one (red) bar left (didn't see a range). Fortunately I just passed a truck stop, and went back and filled up 3.5 gallons at the pump, which refilled it to near full (one bar down from full).

The rapid decline was very surprising. Wondering what would have caused such rapid use of DEF, or if it maybe was just a gauge glitchy thing where the 3 bars was actually almost down to 2, and once the gauge hit one, it flashed the red warning. Any thoughts?

 

[StephenPT]

So I was on a drive last night, some winter/mountain driving, 370mi one way, temps around/below 30 most of the time. Speed between 65-74.

About 60 miles into the drive, I got a 995mi DEF warning. I had about 300 miles to go, thought it shouldn't be a problem. I checked, there were 3 bars left on the gauge. Then about ~90 min later I got a Low DEF warning, one (red) bar left (didn't see a range). Fortunately I just passed a truck stop, and went back and filled up 3.5 gallons at the pump, which refilled it to near full (one bar down from full).

The rapid decline was very surprising. Wondering what would have caused such rapid use of DEF, or if it maybe was just a gauge glitchy thing where the 3 bars was actually almost down to 2, and once the gauge hit one, it flashed the red warning. Any thoughts?

Here's a bit of info about how the gauge works - my guess is that based on your mountain driving (higher load on the engine) the computer used that consumption rate as part of the calculation, which dropped your estimated range faster than the actual miles you had driven.

DIESEL EXHAUST FLUID CONSUMPTION – GM Service Insights

gmserviceinsights.com

 

[Stbentoak]

The gauge is nothing but a guideline and inexacting at best. Best philosophy is when you get 1st warning, dump a 2.5 in from Wally World and move on with life for at least another 6 months unless towing....

 

[drmoose]

Yeah, it seems like my DEF usage is way higher than that all of a sudden. I also feel like I am not getting the MPG I was getting a few months back. I am wondering if it has anything to do with some ECM(?) update that some people have reported. I filled 2.5g a month or so ago, and had driven it about 1k miles since then, and got the low warning. Since filling it a few days ago (to one bar below full) it is already down a bar in ~250 miles. But its really heard to say what that 1 bar meant....

 

[Jellyfrosh]

I've been consuming about a gallon every thousand miles with my LM2 but I've only got 8k miles of data. I also don't tow.

 

[Stbentoak]

I've been consuming about a gallon every thousand miles with my LM2 but I've only got 8k miles of data. I also don't tow.

That's excessive. I've only put 7.5 gal in mine in 19K and its half full now....

 

[Jellyfrosh]

That's excessive. I've only put 7.5 gal in mine in 19K and its half full now....

I live in Wyoming, and I bought the car right at the start of winter weather. Cold temps, mostly highway driving, and often heavy headwind are all it's been driven in. I expect my usage to drop significantly as it warms up.

 

[972sparky]

I have been averaging 2.5 gallons per 5,000 miles. 1/2 city, 1/2 highway no towing.

 

[StephenPT]

Current Miles - 3763
Diesel Used - 140.257g
DEF Used - 2.5g

DEF usage rate - 1.8% per gallon of diesel
Lifetime fuel economy - 26.8mpg

 

[Brand0n]

10,500 mies.
10 gallons of DEF used.

Primarily city driving.

 

[OBSSSD]

I got 8,500 miles out of my first def tank run all the way dry, 21' Yukon Denali XL minimal towing use mostly highway miles

 

[BobHolthaus]

Reviving this thread. Our DEF usage skyrockets when towing. We get the same results as above: 900 miles left, then an hour later (and 80 miles later), we are at 200 miles left. It's completely erratic. Last week it showed almost empty, but then only took like 3 gallons (or so - I don't recall exactly). Now, every time we start the car since then, it pops up with how many miles we have left in DEF range. The odd thing thought is that it continues to count UP over the last week! Started around 200 miles of range (after filling the DEF tank to the overflow point), and today it says there's like 525 miles of range, even though the gauge is almost full. Very erratic. If anyone has a fix, please let me know. Thanks!

 

[JayceeP]

Bumping this as well.

Currently at 3900km on the odometer, or ~2,430 miles. I’ve used 2.5 jugs of DEF fluid, so 6 gallons. Seems like a lot??

Is the usage higher during break in? I just towed a jet ski 400 miles and my DEF gauge showed full (I put one full jug of 2.5 gallons before the trip) over half way through…. I didn’t check it since but with about 50 miles left in the trip I got the check system/DEF error…. *** miles until 104kph/65mph limit… it also locked out my menu in my instrument cluster. So about 50 miles later at home I put ~1.5 jugs, or nearly 4 gallons until I overflowed the def tank a bit (by accident lol).

The check engine light and the menu was still locked… after a bit of driving, the menu soon opened up again (maybe 15 mins of driving). And finally the check engine light went away after at least 30 mins of driving from yesterday and today. So looks like def fluid was the issue.

Is it fair to say usage is higher during break in or is this abnormal? I know I towed a sea doo but 1300lbs isn’t a crazy amount of weight.

Also, the DEF gauge is clearly not accurate at all.

 

[Jay P Wy]

Bumping this as well.

Currently at 3900km on the odometer, or ~2,430 miles. I’ve used 2.5 jugs of DEF fluid, so 6 gallons. Seems like a lot??

Is the usage higher during break in? I just towed a jet ski 400 miles and my DEF gauge showed full (I put one full jug of 2.5 gallons before the trip) over half way through…. I didn’t check it since but with about 50 miles left in the trip I got the check system/DEF error…. *** miles until 104kph/65mph limit… it also locked out my menu in my instrument cluster. So about 50 miles later at home I put ~1.5 jugs, or nearly 4 gallons until I overflowed the def tank a bit (by accident lol).

The check engine light and the menu was still locked… after a bit of driving, the menu soon opened up again (maybe 15 mins of driving). And finally the check engine light went away after at least 30 mins of driving from yesterday and today. So looks like def fluid was the issue.

Is it fair to say usage is higher during break in or is this abnormal? I know I towed a sea doo but 1300lbs isn’t a crazy amount of weight.

Also, the DEF gauge is clearly not accurate at all.

DEF usage is based on engine load (more load =higher NOx), so the higher the load the more DEF it will use. The DEF tank level is like the water and waste tanks on an RV, not a float like the fuel tank. DEF is allowed to freeze so a float would be damaged when the DEF freezes.

FWIW the urea in the DEF is converted to ammonia in the hot exhaust and the ammonia in the SCR converts the NOx to Nitrogen and water (not a complete explanation of how it works).

Edited to remove CO2 and replace with Nitrogen & water.

 

[StephenPT]

DEF usage is based on engine load (more load =higher NOx), so the higher the load the more DEF it will use. The DEF tank level is like the water and waste tanks on an RV, not a float like the fuel tank. DEF is allowed to freeze so a float would be damaged when the DEF freezes.

FWIW the urea in the DEF is converted to ammonia in the hot exhaust and the ammonia in the SCR converts the NOx to CO2 (not a complete explanation of how it works).

Close - it breaks the NOx down to Nitrogen and Water - CO2 emissions are heavily regulated by the EPA and going to continue to get tighter (EPA '27) is the next big emissions regulation. I believe the LZ0 with its revised DOC position, two DEF injectors and other improvements meets the EPA27 requirements for NOx and C02 reductions.

 

[Jay P Wy]

Close - it breaks the NOx down to Nitrogen and Water - CO2 emissions are heavily regulated by the EPA and going to continue to get tighter (EPA '27) is the next big emissions regulation. I believe the LZ0 with its revised DOC position, two DEF injectors and other improvements meets the EPA27 requirements for NOx and C02 reductions.

View attachment 434509

You're right. That what happens when you type something when you just got out of bed and no coffee yet... lol
I edited the post to fix it.