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2020 AT4 gas gauge behavior


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Recently made a trip to OKC and noticed some odd behaviors from the gas gauge.  I generally fill at the slowest automatic rate and then top off to the first click.  Kind of like TFL but I don't wait 30 seconds.  The odd behavior is that the first half of the tank is incredibly inaccurate but the last half is really close.

 

At a trip indicated 104.4 miles and 20.2 mpg the gas gauge indicates full but I should have been down to about 3/4 of a tank or about 18 gallons instead of full (I know just a guesstimate).  Using the myGMC app I had 86% remaining or 20.64 gallons.  I get it there's only a 2.64 gallon difference between the two readings (about 4/16) but the fact that the app was picking up less than full should have been reflected on the gauge since it's the same sending unit.

 

Next check was at 148.4 miles with 14/16 showing on the gauge or 21 gallons.  App indicates 18.3 gallons or 76%. about 4/16 off.

 

180.4 miles 3/4 showing or 18 gallons remaining.  App indicates 16.6 or 69%. about 2/16 off

 

270.4 miles and just between 8 and 9/16 so interpolating... about 12.75 gallons (gauge appears to have resolution down to 1/32 of a tank although only marked for 16ths and 1/4s).  The app indicates 12.24 gallons or 51%. less than 1/16 off.  I filled up at that point and it took 12.01 gallons for a calculated 24.25 gallons in the tank.

 

I repeated this check occasionally at different points on the gauge throughout the trip with the same result.  It's not like a set amount of offset from the gauge but instead a curve? or just a linear offset that doesn't exceed 25% applied only to the gas gauge once you exceed about 60%.

 

 

 

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I don't see anything abnormal here. I worked in the rental car industry for a few years, many years ago. Fuel gauge on the majority of vehicles don't move until its been driven over 100 miles. After that it's playing catchup until it reads empty. The less fuel the more accurate. I don't have a scientific explanation, but suspect it's due to the gas is sloshing around while the car is moving. The more fuel the bigger the wave on the surface, inside of the gas tank. This would cause the float to sit higher.

As for what the app is telling you, I suspect that's more accurate because it's based on what calculations determining how much fuel was actually used. Some will say it's inaccurate, and there's a possibility it's not perfect, but it may still be more accurate than a float on top of sloshing fuel.

Sent from my SM-N960U using Tapatalk

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I have owned 13 GM vehicles over the past 40 years. All do that. It takes about 100 miles for them to move off full. Then slow until 1/2 tank, then the bottom falls out. On the other hand, my Mustang GT will be at 3/4 tank 30 miles into a tank and is slow the rest of the way. My dad drove nothing but Fords and I recall all of his did the same. Even rental GMs are the same way. 
 

Nothing to worry about, just know the once you get to 1/2, prepare to fill up soon. 

Edited by Gray Fox
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I have one that will  move off full rather quick but  when its on empty its Empty and you are about to be stranded. Its much older 2004...   But generally  they take a while to move off full. I think the gauge is off in the  04 express 

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