Fuel gauge still malfunctioning even after complicated reset procedure

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by prius_nerd, Oct 23, 2021.

  1. prius_nerd

    prius_nerd Junior Member

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    Starting in July 2021 (on a drive from Atlanta to Jacksonville), my 2008 Prius's fuel gauge is wildly inaccurate.

    It too quickly drops to just a few pips and even to 1 flashing pip even when I have plenty more gas in the tank.

    So, I searched this forum and found Fuel Gauge calibration | PriusChat which was echoed by How do I recalibrate the fuel gauge - 2007 Toyota Prius and


    I was optimistic that following the (overly complicated) procedure would fix the problem.

    Unfortunately, even having completed the procedure multiple times in the past months, the gas gauge is still inaccurate.

    Do I need to take my car to a Prius mechanic at this point, or are there other steps I can try?

    Thanks so much for your advice!
     
  2. JC91006

    JC91006 Senior Member

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    Use your trip odometer as your fuel reference. The car will safely go 300 to 350 miles per fill up. When you get to that range, fill up your car. Reset the odometer every time you fill up
     
  3. prius_nerd

    prius_nerd Junior Member

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    @JC91006 I appreciate your response and the resourcefulness of that approach! But I want to solve the problem rather than create new chores and risks for myself.
     
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  4. bisco

    bisco cookie crumbler

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    because of the fuel bladder and related pollution equipment, repair may be time consuming to diagnose, and expensive to repair.
     
  5. fuzzy1

    fuzzy1 Senior Member

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    That sounds like a fair-weather Gen3 answer. For some Gen2s exhibiting fuel bladder issues, those distances may be quite risky or even beyond reach for some users and circumstances, especially as cold weather is arriving.
     
  6. JC91006

    JC91006 Senior Member

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    I believe that's a very conservative estimate on a 12 gallon gas tank and a car that averages 40+mpg. But of course, adjust according to you own climate and driving habits.
     
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  7. fuzzy1

    fuzzy1 Senior Member

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    Gen2s with cold or shrunken or folded fuel bladders commonly hold very significantly less than the listed nominal 11.9 gallons. Don't confuse these with 2010 and later models.

    Haven't some experienced as little as 7 usable gallons? Then add in some highway speeds that drop Gen2s below 40 mpg ...
     
    #7 fuzzy1, Oct 23, 2021
    Last edited: Oct 23, 2021
  8. JC91006

    JC91006 Senior Member

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    I haven't really tested the 7 usable gallons theory, until you run empty, you really won't know how much was in the tank. I have to admit I often fill up about 7 gallons from near empty gas gauge, but that is not a good indicator of how much fuel is actually in the gas tank. But to be on the safe side, fill up before 300 and you should be fine.
     
  9. bisco

    bisco cookie crumbler

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    or 250 if your mil is in the car
     
  10. fuzzy1

    fuzzy1 Senior Member

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    Do you have a 2007? The 2010 listed in your profile is not relevant to this thread, Toyota abolished the problematic bladder after the 2009 model.

    And not all Gen2s exhibit a significant problem with this bladder. Many owners find them behaving as they were supposed to. But many others have had real problems with reduced capacity, erratic gauging, and substantial difficulty in adequately refueling. I experienced the later problem myself in a rental, a year before buying my first Prius in 2009 (MY2010).

    ===========================

    PS. Here is how much OP's 2007 is supposed to hold: 11.9 gallons at 'normal' temperature, 10.6 gallons at 14F. But when I first looked at PriusChat in 2008 -- while renting, on the advice of another Prius driver, to learn about this refueling problem I was having -- there were loads of complaints about problematic fuel bladders.

    upload_2021-10-23_18-37-45.png
     
    #10 fuzzy1, Oct 23, 2021
    Last edited: Oct 23, 2021
  11. JC91006

    JC91006 Senior Member

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    I've owned about 20 gen2 cars, so I have personal experience in what you're referring to. The bladder problem is really not that of an issue. I find they are very consistent and no real "bladder" effect on them. If the car consistently takes 10 gallons for a fill up, it will consistently do that. The problem is when I have a car that consistently only gets 7 gallon fill ups (with 1 or 2 bars remaining), but I would just remember that car can only take 7 gallons x 40 mpg. So I would fill up by 300 miles.
     
  12. fuzzy1

    fuzzy1 Senior Member

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    Yes, many owners don't have problem. Especially those always in a warm climate. But the existence of the problem is the very reason I found this forum, the year before buying my first.
     
  13. mr_guy_mann

    mr_guy_mann Senior Member

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    When the fuel gauge reading starts to change rapidly and mileage-fillup testing indicates that it is grossly inaccurate, then it is likely that the fuel gauge level sensor (aka the sending unit) in the tank is failing. On a Gen2 that means you need to replace the fuel tank assembly to correct the problem. It's possible that it could be a wiring fault- you would need to have testing done at the fuel electrical connector to confirm. But be prepared for the cost to replace the tank.

    Posted via the PriusChat mobile app.
     
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  14. Brucetafer

    Brucetafer Member

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    WOW im sorry, but the info didn't copy over like I hoped.. if you have any questions message me and ill try to help, im literally doing this on my 09 touring now and its a complete DISASTER..

    pop the back seat bottom, get to the fuel connections

    INSPECT FUEL TANK ASSEMBLY WITH FUEL PUMP

    1. (a) Measure the resistance between terminals 3 and 7.

      Standard resistance:
      0.2 to 3.0 Ω at 20°C (68°F)

      If the resistance is not as specified, replace the fuel tank assembly.
      1. 44 to 50 psi at idle.

        check the fuel tank pressure sender, .1V-4.9V
        CHECK FUEL TANK PRESSURE SENSOR

        EC–37

        A088404E02

        (a) Inspect the voltage.
        1. (1) Turn the power switch ON (IG).

        2. (2) Measure the voltage between the terminals.

          Standard voltage
        Tester Connection Specified Condition


        1 - 3

        (3) (4)

        4.5 to 5.5 V

        Remove the fuel tank cap.
        Measure the voltage between the terminals.

        A088235E02

        Standard voltage
        Tester Connection Specified Condition


        2 - 3

        (5) (6)

        3.0 to 3.6 V

        Reinstall the fuel tank cap. Turn the power switch OFF.


        Check the Cut-off valve

        Pressure switching valve
        The pressure switching valve located on the canister is used to detect leakage from the bladder tank into the fuel tank. The valve opens during the bladder tank leak check. Then, the fuel tank's fuel vapor flows to the intake manifold without passing the canister.


        If worse comes to it, clean all the grounds.. there's 4-5 in the dash area and I just did mine and they were dirty..

        BEAN, CAN, Combination Meter and ECU are involved in the fuel level process


        ENGINE ROOM RELAY BLOCK, JUNCTION BLOCK
        - INTEGRATION RELAY

        (UNIT B: IG2 RELAY)

        (UNIT C: C/OPN RELAY) - AM2 FUSE
        - P/I H-FUSE

        DRIVER SIDE JUNCTION BLOCK - IGN FUSE
        1. FUEL GAUGE
          • For the purpose of correcting the calculation of the fuel level by the meter ECU, 2 inclination sensors that detect the vehicle's longitudinal and latitudinal inclinations are installed in the meter ECU. The fuel temperature sensor are installed in the fuel tank to detect the temperature in the fuel tank.

          • The fuel level is calculated by the meter ECU in accordance with the signals of the sender gauge located in the sub tank and the vehicle speed signal received from the brake ECU. At this time, corrections are made by the signals from the inclination sensor that detect the vehicle's longitudinal and latitudinal inclinations and the fuel temperature sensors that detects the temperature in the fuel tank. For the inclination sensor centered value setting, refer to the following procedure (see page ME-23).

        2 INSPECT FUEL SENDER GAUGE ASSEMBLY
        1. (a) Disconnect the F14 gauge connector.

        2. (b) Measure the resistance of the gauge connector.
          Tester Connection

          Fuel level

          Specified Condition

          5-6

          Full

          Approx. 4 Ω

          Half

          Approx. 40 to 60 Ω

          Empty

          Approx. 110 Ω

          1. (a) Disconnect the F14 sender gauge connector.

          2. (b) Turn the power switch ON (IG), and check the position of

            the sender gauge needle.

            OK:
            Fuel gauge indicates E.

          3. (c) Connect terminals 5 and 6 on the wire harness side connector.

          4. (d) Turn the power switch ON (IG), and check the position of the receiver gauge needle.
            OK:

            Fuel gauge indicates F.

          5. (e) Measure the voltage of the wire harness side connector.

            Standard voltage
          Tester Connection Switch Condition Specified Condition F14-5 - Body ground Power switch ON (IG) 10 to 14 V



          Standard resistance
        REPLACE COMBINATION METER ASSEMBLY
        3 CHECK WIRE HARNESS (GAUGE - METER)
        1. (a) Disconnect the F14 gauge connector.

        2. (b) Disconnect the C12 meter connector.

        3. (c) Measure the resistance of the wire harness side

          connectors.

          Standard resistance
        4. F14-6 - C10-31

          Below 1 Ω

          F14-5 - C10-15

        CONNECTOR


        REPLACE COMBINATION METER ASSEMBLY
     
    #14 Brucetafer, Oct 24, 2021
    Last edited: Oct 24, 2021
  15. Brucetafer

    Brucetafer Member

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    Also, make sure you fill your car with the ignition OFF.. the car shuts the overflow valve off and allows you to pressurize the bladder to "stretch" it out if its "stiff"
     
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  16. Brucetafer

    Brucetafer Member

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    Ok, after trying to redo my horrid post, I cheated and found this..
     

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