Gas gauge fault - keeps indicating full/empty in tandem

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by SmogSlide, Jul 1, 2013.

  1. SmogSlide

    SmogSlide Member

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    Hello all,

    I couldn't find such a topic in the search, and I apologise if I happen to duplicate the topic.

    In the last few days, my gas (fuel) gauge has been erratic, showing full tank (not long after I filled up) and after 30 mins of driving, it shows empty and beeping at me. The gauge self-healed after a few minutes and subsequently showed the right amout of fuel in the tank. I had this issue once over 3 months ago, but because of the self-healing nature of the issue, I ignored it. But it has becoming more frequent in the past few days... I roughly know how much gas/fuel is left in the tank because I always reset my ODO after a complete fill-up.

    I am suspecting the 12V battery is dying... but OBD II scanner says the battery is 14.6V while car is running so I am stumped.

    Can you guys suggest what the problem could be?

    Also, is there a danger where the car would completely stop because it wrongly detects the car has ran out of gas/fuel?
     
    #1 SmogSlide, Jul 1, 2013
  2. rdgrimes

    rdgrimes Senior Member

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    A 3-year old battery is always suspect, but I'd expect you to see other issues too. I'd have the dealer check it out.
     
    #2 rdgrimes, Jul 1, 2013
  3. SmogSlide

    SmogSlide Member

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    Thanks for the suggestion. I have a session booked this Saturday for a 100,000km service. I was thinking to get them to change the tranny fluid as well, but given this issue broke out, I will get them to do a check. The only issue is that I probably have to prove it in front of them. And with the problem ocurring randomly, it would be near impossible to know when it would happen. Also, it doesn't throw a fault code at all.:mad:
     
    #3 SmogSlide, Jul 1, 2013
  4. phoenixgreg

    phoenixgreg Senior member

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    This is rare, but it could be a sunken gauge float in the tank.
     
    #4 phoenixgreg, Jul 1, 2013
  5. xs650

    xs650 Senior Member

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    That sounds like a bad connection in the gas gauge float circuit. There is a variable resistor attached to a float, and the changing height of the float changes the setting of the variable resistor. If the variable resistor is intermittent, or any connection in that gauge circuit is intermittent it will result in the symptoms you have seen.

    It sounds most likely that there is a bad spot on the variable resistor that the wiper passes over shortly below a full tank.
     
    #5 xs650, Jul 1, 2013
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  6. Former Member 68813

    Former Member 68813 Senior Member

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    Techron concentrate is said to help with the issue (dirty fuel level sensor). Do yourself a favor and start using quality gasoline from now on after you clean it!
     
    #6 Former Member 68813, Jul 2, 2013
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  7. SmogSlide

    SmogSlide Member

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    I always use BP RON 98. Unless the fuel was contaminated, I don't think I could get a cleaner fuel.

    Galaxy Nexus ? 2
     
    #7 SmogSlide, Jul 2, 2013
  8. SmogSlide

    SmogSlide Member

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    It's plausible. If that's the case, the big question is how much would it cost to fix since I am just out of warranty, the labour in Australia is so expensive... this could turn out to be an expensive fix with no fault of my own.

    Luckily I use my fuel card and it shows I always buy my fuel at BP and use 98R. If I have to fight to get it fixed cheaper (or even free), I would!


    Galaxy Nexus ? 2
     
    #8 SmogSlide, Jul 2, 2013
  9. xs650

    xs650 Senior Member

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    Try friendly_jacek's method first. There is a good chance it will work. I've even had an intermittent sender clear itself.

    If you have to replace it, I think it will be very expensive. IIRC, you need to replace the pump/filter/gauge sender unit as a single item.
     
    #9 xs650, Jul 2, 2013
  10. Former Member 68813

    Former Member 68813 Senior Member

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    Not sure of the 98 RON in Australia part, but I did a study on BP 87 AKI (USA) gas oxidation study and BP produced a lot of deposits, unlike Shell 87 AKI gas in a follow up study. I did the study in to find out why I had carb deposits problems in my boat despite Stabil use. From now on, no BP gas for me. I use Chevron/Texaco or Shell only. I can post some images if anyone is interested.
     
    #10 Former Member 68813, Jul 2, 2013
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  11. SmogSlide

    SmogSlide Member

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    I have been told by my mates working in the oil refinery industry that all 91 RON (lowest grade unleaded petrol) in Australia are basically come from the same refinery, i.e. it doesn't matter what brand you purchased it from, it's all the same!

    In the other hand, BP apparently is the only company that guarantee their 98 RON petrol, although I couldn't find any credible source to refer to.

    Having heard what you said, I think I might just try a different type of fuel, maybe Caltex, to see if it makes a difference at all.
     
    #11 SmogSlide, Jul 3, 2013
  12. Former Member 68813

    Former Member 68813 Senior Member

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    1. It's true that basic fuel is not brand specific. It's the cleaning/stability additives that are added separately for every brand than make a huge difference.

    2. Now, if BP guarantees their fuel indeed, ask them to clean your sensor.

    3. Changing fuel brand is not going to fix anything. You need to CLEAN it.
     
    #12 Former Member 68813, Jul 3, 2013
  13. phoenixgreg

    phoenixgreg Senior member

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    Here's where I think the fuel pump and sensors are located. You'd need to extract the back seat to get access to the panel shown here. I discovered this while doing my Dynamat project. If it works as I suspect, at least you or your mechanic would not have to drop the tank.
    Dynamat - all removed thru LR door.JPG
     
    #13 phoenixgreg, Jul 3, 2013
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  14. rdgrimes

    rdgrimes Senior Member

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    Gosh, the noise proofing treatment on that floor pan is mighty sparse.
     
    #14 rdgrimes, Jul 3, 2013
  15. phoenixgreg

    phoenixgreg Senior member

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    Have a look at my Dynamat project from last October. Sadly for all the work it did not totally dampen road noise:
    Dynamat 2.0 | PriusChat
     
    #15 phoenixgreg, Jul 3, 2013
  16. SmogSlide

    SmogSlide Member

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    Yeah will do that too. Just found out where to buy some Techron 5000 and will pick two up tonight. Cheers!

    Galaxy Nexus ? 2
     
    #16 SmogSlide, Jul 4, 2013
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