Fuel gauge recall 2018 - Page 2 - Subaru Outback - Subaru Outback Forums
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post #11 of 312 (permalink) Old 11-09-2018, 08:00 AM
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Originally Posted by rallysquirrel View Post
That's always productive, especially calling people idiots

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I know, I was really offended when someone called me an idiot for not testing the limits of my fuel tank. <sarcasm>

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post #12 of 312 (permalink) Old 11-09-2018, 08:44 AM
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The trade journals make mountains out of mole-hills to sell hits to their web sites. It is a programming flaw (bug) in how the low fuel indication and miles-to-empty values are calculated. It is fixed by pushing new firmware in to the computer.
I've seen a couple articles now where it's called a "stalling" issue. My sister in law actually sent a similar article to me and was all concerned... I'm like, no. It's just a software bug, it'll get fixed soon, and I'll be fine because now that I know, I'll just fill up when I get close to a quarter tank. Some of these articles make it sound like our cars are just going to stall randomly for no reason!

And yes, I found the bug myself the hard way. Almost. I had "30 miles remaining", and managed to put 18.3 gallons of gas into my car. Talk about shaving it close! Ever since I've had the car, I'd noticed that I was putting more gas in than the car indicated. Asked the dealer about it, and yeah, known issue. Ah well. Glad they're fixing it, so I don't have to lecture everyone who drives my car to not trust the fuel gauge!

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post #13 of 312 (permalink) Old 11-09-2018, 08:55 AM
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Originally Posted by Tishers View Post
The trade journals make mountains out of mole-hills to sell hits to their web sites. It is a programming flaw (bug) in how the low fuel indication and miles-to-empty values are calculated. It is fixed by pushing new firmware in to the computer.

There will still be a large number of people who imagine that the dash board will be disassembled or the gas tank will be dropped to do major surgery on the car.

You are always gambling whenever you are depending upon some display that tells you "11.2 miles to empty" and then you get bent out of shape when it conks out 3 miles later. It's like "OMG! how could they do this to me! if I only had those additional 7 miles I could of prevented that accident officer!"

I'm almost to the point of astonishment that this is an issue, personally--between people freaking out about it being a safety issue, people who rely on a guesstimate of miles remaining based on mpg, etc (if you think it's any better than that, I'm sure I've got something here I can sell you), and folks that think some major fix (beyond a simple software update that makes a calculation slightly differently), it's somewhat...frightening to me. I mean, there was once a time when the needle on the dash was all you had to go by, not "xx miles" left, or light to remind you that you haven't been paying attention. I've personally had a habit of figuring out about how much gas is in my car when the needle gets just above a quarter tank--fill the car up, subtract amount of gas put in from total fuel capacity, and now you know about how much further you could have gone...and from there, who cares what light is on what says "xx miles". People should be using their brains when they drive a lot more than they do. :-/
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post #14 of 312 (permalink) Old 11-09-2018, 09:55 AM
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Available fuel is based upon a measurement of level in the tank. It is not quite as simple as saying that 12 inches equals 10 gallons so 6 inches equals 5 gallons or 3 inches equals 2.5 gallons. That type of calculation is based upon a cylinder or a cube where there isn't any usual contours to the walls or the floor of the tank. The fuel tank in a Subaru is an irregular shape and as it gets narrower near the bottom there is much less fuel left based upon depth of the tank.

To measure this type of tank you either use a mathematical formula to calculate the volume (like with an sphere or a pyramid) where the shape is regular. A gas tank in a car is irregular, there there is a tapered floor and a lower area (in the world of tanks, this is known as a sump). To determine the value of this type of tank based upon depth you would use something known as a "strapping table" that is based upon actual measurements of remaining fuel based upon depth. Then this strapping table is built in to the fuel calculation code and you allow the code to interpolate values between the lines in the table. It roughly approximates the true value (more accurate when there are more entries in the strapping table).

I can see where someone let a less diligent engineer make some assumptions to the programming (maybe they did not use enough granularity in the table) or they have a zero vs. span problem with the sensor (that happens too). Usually you can get pretty darned close by calculation and generic tables; to be super-accurate someone would need to calibrate the depth sensor to each individual tank (that is NOT going to happen).

I am a geek; I was a process controls engineer for many years and this was the kind of stuff that I did every day.
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post #15 of 312 (permalink) Old 11-09-2018, 10:20 AM
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FWIW, I typically fill the gas tank on my 2018 Outback 3.6R Limited when the miles to empty gauge indicates 40 miles. My typical fill-up gallons is 17.5 gallons which theoretically means that I have 1 gallon left in the tank. Assuming an average of 20 miles per gallon the MTE gauge is reading 20 miles too many. This info might help others avoid running out of gas.

My $0.02. YMMV

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post #16 of 312 (permalink) Old 11-09-2018, 10:25 AM
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I can see where someone let a less diligent engineer make some assumptions to the programming.
Less diligent engineer.... LOL, nice euphemism for "incompetent" or one that just got of the boat from some third rate engineering school in a country where cows are the primary form of transportation.

What I find interesting is that this little "bug" wasn't discovered during any of the typical new model/model refresh validation testing of any of the software? No one said anything about filling up 18 gallons of gas when the DTE still said 70 miles? None of the test engineers ran out of gas with 30 or 40 miles left?

I'm not an automotive engineer, but still deal with wheels, engines and meter panel/VCM/ECM systems. I can totally see how something like this could get missed, overlooked, ignored, blown off, etc. Way too many engineers rely on "the computer said it would work" rather than real world wrench turning and testing.

Luckily it's only the gas gage. People can die over stuff like this when it's a little more serious.
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post #17 of 312 (permalink) Old 11-09-2018, 12:37 PM
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Originally Posted by martin_j001 View Post
there was once a time when the needle on the dash was all you had to go by
Yes and as someone who has had cars from the 60's 70's 80's and 90's those needles also hit E and just below and you had enough fuel to go a ways. It didn't mean you should or it was the smartest maneuver to perform.

But the overall theme of E means you have a gallon left was still followed. You can bet if those cars ran out at 1/4 tank when car was still relatively new people would have rightly thought it was broke or a safety issue.

Totally different from running out when car is telling you you have a gallon or two left in the tank.
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post #18 of 312 (permalink) Old 11-09-2018, 02:17 PM
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It boils down to the old "accuracy vs. precision" issue. Old school fuel gages were not very precise. You had no way to know whether you had 2 gallons or 3 (or 1). However, they were largely accurate in the sense that if the needle was sitting on "E" you'd better get your butt to a gas station because you probably only had a gallon or two left. People who weren't willing to gamble never flirted with "E" on a regular basis.

Now, give someone a clear number on how far they can drive before the car runs out of fuel and the story changes. By gosh if the car is smart enough to know how many miles of range are left it must be accurate because it is precise in saying exactly how far you can go, right??? Shoot, I might have even gambled on it to get to work and back if it said 50 miles to empty because it's only 38 miles round trip. Glad I didn't try it because I'd have been walking.... The issue is while the display is precise, it is far from accurate, and "false precision" is a real gotcha for anyone involved with data and numbers.
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post #19 of 312 (permalink) Old 11-09-2018, 05:49 PM
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Several threads about this already in the Gen 5 forum...


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post #20 of 312 (permalink) Old 11-12-2018, 11:39 AM
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https://www.consumerreports.org/car-...ct-fuel-range/

opened this thread for a little while. and made it a sticky so people can find it and link it.

will some polite 2018 owner person post the text of the recall.



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Found a Subaru Vin Decoder (also works on many manufactures):
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