Fuel Gauge calibration

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by richapple, Jan 22, 2018.

  1. richapple

    richapple Junior Member

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    2006 Prius... Switched out the 12V battery (yes, 2006 to end of 2017 - not bad) and though I was able to reset my few customizations (seat belt beep, a couple others), the gas gauge got set to empty. I probably had about a quarter of a tank of gas at the time.

    Now the tank shows full after a fill-up, but goes to empty and then blinking/add fuel way before needed. (Used to be pretty spot-on.)

    I find the following and will try it, but does anyone know if this is what I need to do for this "electronic reset" that disconnecting the 12V battery caused? (I did try something like what I'll copy and paste below, but it didn't work and may have been slightly different.)

    From another post:

    from rick57 over on the old site:​

    Ok everybody,sorry this has taken to long. Been busy with a lot of things going on and I forgot, Embarassed . I had a new 2G Prius in for PDI and decided to give it a try. And guess what,I found out what we were doing wrong! Just one little step messes up everything. Here is the steps from the TSB and only applies to the 2G.

    1. Park the vehicle so as it is level,front to back and side to side.
    2. IgOn and make sure that "Trip A " is showing on the odo ( this is where we made a mistake Embarassed ).
    3. Power down.
    4. Keep your foot off the brake.
    5. Push in and hold down the Odo/Trip button.
    6. Push the Power button twice to IgOn ( not Ready mode ).
    7. Turn the Odo/Trip off then On 3 times in 5 seconds.
    8. Continue holding the Odo/Trip button until a 6 digit code appears.
    9. Release,then push again the Odo/Trip button for another 5 seconds. The 6 digit code will change to a 5 digit code.
    10. After the middle digit,of the 5 digit code,changes to "1" release the Odo/Trip button and the odometer will return to normal reading.

    Hope this clarifies the steps.

    _________________
    Rick Angles
    Toyota Master Diagnostic Technician
    Toyota Hybrid Technician
    Germain Toyota
    Columbus, Ohio​

    If someone has done the above procedure, my only question would be for the end of step 9 and then step 10. Does this mean that once the 6 digit code changes to a 5 digit code you keep holding the Odo/Trip button down and that 5 digit code will keep changing? When the middle digit becomes a "1" you then release the button?

    When I tried something similar before, I was moved to display a middle digit of my own...

    Any pointers appreciated,
    Rich
     
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  2. bisco

    bisco cookie crumbler

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    wow, that was a great run!

    are you sure you lose the gas gauge when the 12v is down? i have never heard that before.
    how many miles on her?
     
  3. richapple

    richapple Junior Member

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    86,000 miles. I can't say there was an absolute cause/effect for the gas gauge going wacko, but it was off its rocker for the first time ever right after the new 12v was connected.
     
  4. bisco

    bisco cookie crumbler

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    yeah, that would be quite a coincidence.
     
  5. Dr I A Ball

    Dr I A Ball New Member

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    Having just purchased a 2007 Toyota Prius I have encountered the bizarre issue of the notoriously inaccurate fuel gauge – after filling the fuel tank the first “pip” didn’t disappear until the vehicle had travelled 180 miles!

    In its later versions of this car Toyota has abandoned the Fuel bladder in favour of a conventional resin/plastic fuel tank with a normal float system of measuring the fuel remaining; the fuel bladder being employed in aircraft and racing cars to avoid the dead space above the fuel where fuel vapour can accumulate and therefore exhaust to the exterior causing atmospheric pollution and increase the risk of explosion in the event of an accident!

    So I conclude that the only way in which the remaining fuel can be measured is by the on-board computer! The fuel is injected rather than vaporised as in a carburettor and therefore the quantity of fuel used per second can be measured; the odometer tells the Engine Management Unit [EMU] the distance travelled per second and this enables the computer to calculate the MPG continuously shown on the display second by second.

    So the quantity of fuel used shown by the 10 “pips” on the fuel gauge is actually not measured directly but computed, and this is why this measurement can be put out of kilter if say the battery is disconnected without maintaining a power supply and the settings for the fuel levels are lost. This is why the cure to reset the fuel gauge is a complicated electronic manoeuvre using the odometer Trip A reading and the ignition on/off buttons with the vehicle stationary on level ground.
     
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  6. Dr I A Ball

    Dr I A Ball New Member

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    Since writing this piece I have found a comprehensive article about the construction and operation of this unusual type of fuel tank. My assumption that it would not have a float mechanism was wrong. There is a separate mini-tank alongside the main bladder tank which operates much as the water level indicator on a kettle. This conveys the information to the fuel gauge in the conventional way by electronic signal. Unfortunately the design leaves it prone to inaccurate interpretation of the level of the fuel in the main bladder tank if for instance it is refuelled with the car on a steep slope and this is not always easy to correct afterwards - the article in question is entitled

    It appears your Web browser is not configured to display PDF files. No worries, just click here to download the PDF file.

     
  7. NikosG

    NikosG New Member

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    I have a 2008 Prius with 117,000 miles. Everything worked fine until last September when the gauge would show empty after only 200 miles or so . . . I went to my (no longer) trusted local dealer, who charged me some nice change to recalibrate the gauge, only to find out that they had done nothing. They had a second try only to make it worst so that it would start showing empty at 150 miles!

    I used to be able to use at least 8-9 gallons of the tank on a regular basis but now we regularly refill with 4-6 gallons at best as my wife is concerned about running out of gas. We regularly monitor MPG vs miles driven so I guess we could drive it until we know we have used 10+ gallons but we are concerned about the possibility that the bladder system fuel "tank" has deformed and we do not want to run out of gas.

    My local Toyota dealer has been very defensive about it. Actually, last time I was there I was invited to talk with a team of managers and I was given a very formal speech being told how they did everything by the (Toyota) book and that if I wanted it really fixed, they could replace the tank for a couple of thousand dollars or so.

    I used to swear by Toyota products but not anymore, especially with the way I was treated. I would have been OK if they told me up front they could not fix it but NOT when I had to pay for it and they acted like nothing happened!
     
  8. d lichty

    d lichty Junior Member

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    My mechanic says to try pulling the fuse on your dome light for a few seconds, then plug it back in. this only works on the gen2...
     
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