Fuel Gauge Driving Me Nuts

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Hybrid Hobo, Jul 12, 2022.

  1. Hybrid Hobo

    Hybrid Hobo Member

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    Don't know if it's my cluster that's the issue, or the fuel bladder itself, but bottom line is, dealing with the gauge on my instrument panel is a royal PITA. Now I know why they call it the "guess gauge"!

    Not only do the pips/bars occasionally go higher & lower, but I really don't understand the deal with the gasoline amounts. First off...

    As I live out of my car on extended camping forays, the a/c is on about 23 hours per day, since temps here in the NE have been in the 80's & 90's with excessive humidity. Of course...

    I realize that this excessive usage obviously burns more fuel, but prior to getting the Prius I read in numerous places online that with the a/c on low, that the car might burn maybe a half gallon of gas per night. Double that if used during the daytime hours too, but it seems like it's burning much more than that. Case in point...

    I went to sleep the other night with about 4 or 5 bars showing on the gauge. Usually, I use 2 or 3 bars overnight with a temp setting of 65 to 68 and the fan on low. This seems like a lot to begin with, but this time disaster almost struck! I slept a few hours longer (about 9 hours total), and was laying in the back after rising answering work emails when I heard a beep. I looked at the instrument panel and noticed that the low pressure icon (which wasn't on the night before) was lit up, and I was down to one bar on the gauge...which was blinking! I immediately shut the car and assessed my options. I could call AAA and get a few gallons of gas delivered, or try making it to the station which was 3 blocks away. I chose the latter and made it there just fine (thankfully). Though, I've read where people have driven 25 miles with a blinking bar, and some have stalled within a few blocks. Guess I got lucky.

    Here's the stranger thing though - and my main question...Assuming I was near dead empty, I thought the Prius held about 11 gallons of fuel. I put $20 in the tank (about 4 gallons worth) and the gauge went all the way to full! So...

    Was I indeed near empty? If so, how could the fuel gauge show a full tank after adding just 4 gallons of gas going into an 11 gallon bladder capacity? Where did the other 7 gallons of fuel go?

    Still not sure if the beep I heard was the tire pressure icon going off or the blinking fuel gauge, but I'm EXTREMELY lucky it didn't happen at night, as I'm a heavy sleeper, and would've surely awoke to a dead car in the morning.

    ***Usually when I fill up the tank, it cost about $28, which equals about 5.5 gallons of gas. That 11 gallon capacity is either wrong or my gauge or bladder has gone haywire.

    P.S. - Can someone please explain how to check my miles per gallon/fill up using the energy screen. I'd greatly appreciate it.
     
    #1 Hybrid Hobo, Jul 12, 2022
  2. bisco

    bisco cookie crumbler

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    unfortunately, there's just no way to do that on a gen 2.

    that being said, there is some kind of vent on the metal part of the tank that lets air out as you fill the bladder.
    i would investigate that first, and if that isn't the problem, replace the tank.

    have you tried all the recommended practices for filling a stubborn gen 2?
     
    #2 bisco, Jul 12, 2022
  3. Hybrid Hobo

    Hybrid Hobo Member

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    Thanks, Bisco. Not only am I NOT a car guy, but I'm also disabled due to a stroke, so my ability to get into things is limited. Again, not even sure if it's the instrument cluster that's the problem or the fuel bladder.

    What troubleshooting/testing methods are there?

    P.S. - I thought there was a way to track my MPG or trip data through the information screen? I'm trying to figure out (even a ballpark) how many total miles I'm getting per a full tank fill up.
     
    #3 Hybrid Hobo, Jul 12, 2022
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  4. bisco

    bisco cookie crumbler

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    the screen gives you average mpg, and you can use that divided into miles driven. but when camping, i don't think there's a way.
    you might try tracking how many gallons you put in each morning, and using that as a gauge for future usage.
    in a properly operating gen2, the manual states the total capacity, part of which is emergency funds, after it beeps and the last pip is blinking. i think it's around 2 gallons.

    but when the bladder starts acting up, all of that is out the window.

    i don't see how it could be the gauge. if you were filling the tank, it should use all of the capacity before the emergency part, and then ten it beeps.

    most people who can't get more than a few gallons in have a bladder problem.

    one experiment you could do is have a 3+ gallon spare gas can with proper nozzle to open the filler vent cap on hand.
    fill the tank and let it run until it's out of fuel.
     
    #4 bisco, Jul 12, 2022
  5. PriusCamper

    PriusCamper Senior Member

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    I think you're making yourself crazy staring at the guess gauge... Also, it sounds like your bladder needs to be stretched out to boost fuel capacity. Filling the tank as much as possible and driving the car all day in super hot weather is how I've done it successfully. If I were you I'd fill your tank every day, even if its just a gallon so your gas gauge is always indicating a full tank. By the end of Summer your rubber bladder will for sure be back to full capacity and you'll no longer be in the habit of looking at your gas gauge too often.
     
    #5 PriusCamper, Jul 12, 2022
  6. bisco

    bisco cookie crumbler

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    #6 bisco, Jul 12, 2022
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    I would suggest taking notes as to how far you travel (or how long you park with A/C on) when the fuel gauge drops for bar. See if it drops very quickly from a certain level (4 bars, 8 bars, whatever) to flashing ("empty" warning).

    I say this because the last couple of Gen2 fuel tanks I replaced were due to the level sensor going bad. If the sensor wears and has high resistance or an open circuit, the gauge flashes.

    The test would be to have someone pop the rear seat bottom out when the gauge is flashing. Remove the little access panel, unplug the tank connector and measure the level sensor resistance. The bad ones were way over 110 ohms. (that's the "highest" reading it should ever have)

    Also as mentioned, there could be a problem with the fuel tank "vent". Like any closed vessel, you can't put liquid in(to the bladder) if air can't get out (from the space around the bladder). Read up in the service manual about the evaporative emissions system if you want to learn more. It's a bunch of valves and plumbing that collects vapors from the tank and feeds them into the ICE. It also has to self test the entire system for any pinhole leaks.

    It's complex and hard to access. Not many shops can diagnose these systems correctly. (It really helps to have a lift, and specialized testing gear).
    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, Jul 12, 2022
    Last edited: Jul 12, 2022
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