Def usage - seemed to drop really fast

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drmoose

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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

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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.

 

Stbentoak

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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....
 
OP
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D

drmoose

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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

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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.
 

StephenPT

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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
 

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