False Fuel gauge readout?

Easter Egg Time! Want to reset the inclination sensor on your 04-07 Prius? (thats the little thingy that tells the computer what angle the fuel tank is sitting at so it calculate where to set the gauge.

1. Make sure you are on a level surface!!!
2. You must have between 1/4 and 3/4 tank of fuel!!!
3. Re check steps 1+2!!
4. Make sure "trip A" is showing on ODO and press down the parking brake
5. DO NOT STEP ON THE BRAKE PEDAL!
6. Have Power off and press and hold the ODO/Trip button.
7. Press Power two times. NO BRAKE PEDAL!!
8. Release ODO button three times.(You were holding it down, release #1, press, release #2, press, release #3.
9. Press and hold ODO 5 seconds. ODO display should change to 066060 (or something simlar, should look like gibberish)
10. Release and press ODO again and hold until display changes by one digit (such as 066160)
The actual digits are codes for the ECU to interpret. Once the display has changed, release the button and drive normally. Don't forget to remove the parking brake!

The ECU calculates fuel level based on many factors. One of them being is the tank level? Remember, Prius has a bladder so it cannot have a normal float type device. Also the bladder expands and contracts with differing fuel loads (to help reduce evaporative emmissions) and is temperature sensitive.

 

<div class='quotetop'>QUOTE(Bear68 @ Jun 21 2007, 12:24 PM) [snapback]465985[/snapback]</div>

and from qbee42: "Partial fills will throw off fuel computers on many cars. When you do a partial fill, the system has to work on just the float level, which is never completely accurate, and really bad on the Prius. Follow the previous poster's suggestion and fill it up."


I was not aware that the fuel gauge had to be reset after fill up. Until Bear68 said that there was no float sensor because of the fuel bladder system, I had thought that a float sensor was providing the data for the fuel gauge. What type of sensor does the Prius use to provide fuel level info for the gauge? Apparently the inclinometer provides an input to this system, but what tracks the fuel level? Further why does it not work on occasion if the tank is not completely full? Is the fuel level tracking system described in the shop manual?

If the fuel has to reach a specific level to reset the fuel gauge, why can't this feature be used to determine if the tank is full on those occasions when the nozzle keeps clicking off before the tank is full? There seems to be some ambiguity in the system, but it is not clear to me what it is.

 

<div class='quotetop'>QUOTE(RapidRobert @ Jun 21 2007, 04:10 PM) [snapback]466075[/snapback]</div>

There is a float type sensor. It is inside the metal "fuel Tank" in a container (along with the fuel pump) but external to the bladder which is also in the metal fuel tank. See http://priuschat.com/index.php?showtopic=31545&hl= courtesy Galaxee.

The reset on the mfd only resets the display (miles/mpg) not the fuel quanity system.
-----
Harry
2005 super white

 

The procedure Bear68 described is usued to recalibrate the gauge in the event that it is not functioning "normally". For example, if it never shows 10 pips when full. The erratic disappearing of the pips, as stated by everyone, is normal and is no worse than the analog gauges in our other cars.

If one pumps a small quantity of gas into the tank the difference in volume does not (at least) immediately register on the huess gauge. My only experience was pumping some 2.7 gallons at the end of the rally. The gauge did not show 10 pips when I started the car and left the gas station. The 10th pip appeared either the 2nd or 3rd time the car was started.

 

<div class='quotetop'>QUOTE(JimN @ Jun 21 2007, 05:03 PM) [snapback]466103[/snapback]</div>

Your experience seems to be different than the OP who went for 3 days without the gauge changing from a single pip. I am trying to understand why the gauge requires a certain "volume" before it registers any increase at all. Most of the time it works properly, but occasionally it doesn't move at all. For some people, it apparently requires a fill up to register an increase in the volume of gas in the tank. For others it doesn't register until the car has been restarted multiple times. This is puzzling to me. Is it possible that the float sensor gets wedged and only breaks free when the tank is filled or the car is driven over a rough road? The fact that one post said that the car had been driven 200 miles without any change in the number of pips suggests that road vibration may not be enough to free the float - if that is the problem.