HELP! My gas gauge is suddenly demon possessed!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by FrankD, Sep 11, 2019.

  1. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Hello all! It has been awhile since I've posted. I still have my 2007 Prius, now with about 183k miles. Suddenly, my gas gauge is all wonky. I never let it go below 3 bars. Last week because of the hurricane, (which for us was nothing), I MIGHT have overfilled it. I am not sure. A few days later, it was down to about 1/2 a tank, no problem. The next day however, it went from a 1/2 a tank to ONE bar. No evidence of any gas leaking. I went to fill it up and it only took like 4 gallons to fill it.

    This was 2 days ago. I drove it maybe 120 miles yesterday and I think it showed only one bar down. Today we drove the car about 60 miles and it showed ONE bar blinking! We went to the gas station and refilled the tank and it took 5 gallons.....so it clearly was NOT at one bar.

    So...my question is, 1) How do I fix it? 2) Will the car do anything else goofy like shut down if it THINKS it is out of gas, when it is not? 3) Is it time to finally get rid of the car I've really liked for like 10 years? 4) As long as I keep a gas log so I know when to fill up, can I keep driving it?

    Thank you in advance for your good help. I do not think I am loosing gas at all, I think it is a sensor problem or something.....

    Frank D.
     
  2. pasadena_commut

    Joined:
    May 2, 2019
    182
    47
    0
    Location:
    Southern California
    Vehicle:
    2007 Prius
    Model:
    N/A
    The sending unit in the gas tank may be broken. I have no experience with that in a Prius but long ago one of my cars did something similar when that part broke. In that car it was basically a large variable resistor, with a wiper that went up and down a metal coil 1:1 with the gas level. The wire broke on the coil and all sorts of crazy things happened. It worked when the tank was nearly full once it dropped below a certain level the gas gauge would go to zero or dance around.

    In normal cars this is usually an easy part to replace. However, as this is a Gen2 Prius and it has that bizarre bladder in the gas tank, it might also have some peculiar type of sending unit.

    There is a calibration procedure you could try, just in case it is some electronic glitch. Can't imagine it would make things worse:

    Fuel Gauge Calibration Instructions | PriusChat
     
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,149
    6,186
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Frank, your 12V battery is probably near death. When voltage on the 12V bus drops too low the fuel gauge system will lose its memory of the fuel level and the blinking one bar results until the system is powered up and has a chance to assess the actual fuel level.
     
  4. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Wow...thank you Patrick....I am on my 3rd 12v battery, the last two have been optima's....the current one is about 2-3 years old. I will check that asap. Others have posted about recalibrating the fuel gauge. I will check the battery. Here is a dumb question...if I go to the auto store, where they check the battery with a hand held thing....and they also check it under load....can they do that using the terminals under the front hood, or do they have to check it from the battery itself in the back.....just asking because I carry a lot of tools, etc....would be a bit of a pain to take everything out of the back to get to the battery...although I would have to if I need to change it. Bummer....I was thinking of perhaps trading it in within a month or so.....hate to throw more money into it now, but it could be worse.

    Can I still drive it for the next few days without worry...? I might not be able to work on it and do this until the weekend, but still need to drive about 150 miles with it in the next two days or so.....Thanks!!
     
  5. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Actually, I bought the current battery on 12/27/16 from Amazon...so it is about 2 and 3/4 years old. Then it was $167, now it is $238.....
     
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,149
    6,186
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    I believe it is necessary to remove the battery to do a load test.
     
  7. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Thank you Patrick...you are always such a good help here. I do see that Amazon has a 3 year warranty on the purchase....so I will have the battery checked for possible replacement. The car starts and runs fine, except for the wonky fuel gauge....do you think it is safe to drive for a couple of days? This just started occurring. Thanks! Also, if it is not the 12v battery, would you have other opinions as to what to do?
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,149
    6,186
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    It may be safe to drive but you should have a Plan B to deal with a no start due to a failed battery.

    If the battery is not the issue then you can try resetting the fuel gauge calibration but I am not optimistic that would help.
     
  9. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    I actually just got off the phone with amazon and they are sending me a new battery to be delivered Friday at no charge at all. Hopefully that will solve the issue......here in Florida, most batteries die after about 3 years due to the heat. Thanks! will keep you posted!
     
  10. NoThrowningRocks

    NoThrowningRocks Junior Member

    Joined:
    Jun 16, 2019
    29
    12
    0
    Location:
    Atlanta, GA
    Vehicle:
    2006 Prius
    Model:
    II
    Frank, can you please point me to instructions on how one conducts a full load battery test (and test the HV battery)? I have Techstream and read through parts of the Help section but couldn't find it there.

    Lol, Amazon is great. Patrick has been a HUGE help to me also. He's been dead right far more often than not, so I hope it's the battery and you're on your way once again!
     
  11. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Dear NoThrowningRocks, I seem to remember some way to do a test that showed up on the screen, but I've forgotten, and could be wrong. Now that Amazon is sending me a new battery, I will just replace the battery Friday, and take the "old" one down to the local shop to test it. Most all places can do that. amazon told me not to return it or anything, so we will see if the new battery helps. I do not know if there is any test for the big battery.....I've got 183k miles on mine, so I just drive with my fingers crossed. I agree Patrick is great! I am hoping he is correct with this one....
     
  12. NoThrowningRocks

    NoThrowningRocks Junior Member

    Joined:
    Jun 16, 2019
    29
    12
    0
    Location:
    Atlanta, GA
    Vehicle:
    2006 Prius
    Model:
    II
    No worries, I'll keep searching. I had an engine failure (long story) and the mechanic who replaced it put one in without a VIN. In Georgia, car part VIN alteration/removal is against the law, so the thinking is the engine was stolen (local police agree after posing several "hypothetical situation" questions to them).

    I'm running into more problems and concerned he may have switched my HV battery, so wanted to test it

    Good luck!
     
  13. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Patrick, would it still be the battery if the fuel gauge in one trip of say 15 miles drops bar by bar to one last bar, then blinks? The new battery will be here tomorrow, and in Florida it is good to replace batteries every 3 years either way, but just wondering, as it never went right to blinking one bar, but creeped down to it. Thank you!
     
  14. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    NTR...wow. Mine has been great, just do not know when to let it go or keep it....
     
  15. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,149
    6,186
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Try the fuel gauge calibration.
     
  16. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Thank you Patrick. Since they are sending me a new battery I will also do that.
     
  17. wjtracy

    wjtracy Senior Member

    Joined:
    Sep 19, 2006
    10,909
    3,383
    1
    Location:
    Northern VA (NoVA)
    Vehicle:
    2006 Prius
    Our 2006 at 185k miles has been doing this sporatically for a year or two now.
    We just had a bout if it and we were worried but no problem lately.
    I suggest check oil make sure it is not low, seems funny but try that too.
    Our 12v batt is fairly new Optima but short trips these days could take a toll.

    Our MFD touch screen is largely disfunctional (re: touch feature) so I don't know if we can do calibration procesdure but I did try it a few years ago.
     
    #17 wjtracy, Sep 12, 2019
    Last edited: Sep 12, 2019
  18. pasadena_commut

    Joined:
    May 2, 2019
    182
    47
    0
    Location:
    Southern California
    Vehicle:
    2007 Prius
    Model:
    N/A
    You can check the battery voltage using the MFD. Here is a demonstration:

     
  19. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    Thank you for that video....I remember doing this years ago, but forgot how. Thanks! I will do this. Yesterday I filled up the car, and today I drove 175 miles.....the display shows 2 bars down.....seems normal. The MFD shows about 45 mpg.....normal now here in Florida with the A/C blasting. Will keep you all posted. I very much appreciate all of your kind help. Respectfully, Frank D.
     
  20. FrankD

    FrankD Member

    Joined:
    Apr 21, 2009
    199
    39
    0
    Location:
    Leesburg Fl.
    Vehicle:
    2007 Prius
    Model:
    N/A
    So...I just did the check...the MFD showed 12.3 not under load. I did then power it on, with A/C blowing, and it went UP, not down, to like 14.3. SO....is that good? Is my battery ok..? The fuel gauge seemed better today, so perhaps everything is good...(for now)..? Is 12.3 ok?

    Thanks! Frank D.
     
Loading...