Fuel Gauge Drops from 2 Bars to Blinking Very Quickly

welcome!
you might just need to recalibrate it. see if you can find directions using the search function, or youtube. i doubt there's anything wrong in the tank.

 

You do come up with some interesting comments sometimes.
Since when has one been able to "recalibrate" a fuel gauge.......or pretty much ANY kind of vehicle ??

Answer to the original question:
Fuel gauges are notoriously inaccurate and typically drop faster near the end.
They usually are "repeatable" though.......so that once you find out how much is really left in the tank when it hits E, that much should be left every time it gets to E.

Note: There is no good reason to let it get that low. There are several reasons to start looking for a fill when it gets to about half.

 

what was i thinking, googling it doesn't come up with any hits.

 

First because human beings have a LOT of things on their plate to keep track of........and starting to think about getting gas at half should mean that you actually DO it around a quarter or so. If you wait until it is near or on E, your margin for error is GONE.

The more empty space you leave in the tank, the more condensation (of water vapor) is likely to happen, just in general.

And yes, I tend to be "extremely conservative".......except where it comes to politics in the U.S.

 

FWIW, I start looking when I get to a quarter of a tank, and then I wait until I see something convenient. Unless I'm going out of town in the morning, or traveling in some forsaken place like Wyoming or the Dakotas. Sorry Wyoming and Dakota people. No disrespect intended, but geez some of those stations are so far apart I had to carry a gas can on my motorcycle to make it to the next one!

 

I have a Gen2, but 8-9 gallons is normal fill-up from empty and I only get 6-7 gals these days.
Also the fuel gauge is not linear. First bar can be 150 miles.
Then you start losing bars every 25 miles, some longer, some shorter.

 

G'day,
All my recent Toyotas have had the same response.
They're being 'better safe than sorry'.
David S.

 

are we discussing the large reserve, or the op's trouble with the last 2 bars?

 

... at least since the Gen2 Prius has been available. But I'm not recalling anything similar for the Gen3, so Bisco may be confusing generations.

Here is what is normal for a typical Gen3 Prius Liftback, without your gauge anomaly. Out-of-gas ought to be 100-ish miles beyond the point where DTE reaches 0 miles, but this can be highly variable depending on conditions.
[WARNING] Running out of gas (Gen III) | PriusChat

 

For what it's worth, my wife and I had this new Honda Odyssey that had a similar problem. The first 3/4 of the tank would read normally, then the gauge would drop abruptly to zero.
I'm a EE and I troubleshoot recalcitrant hardware for a living. As it happens, I always buy the service manual for a car, unless that car is from Toyota. So I popped the manual for the Odyssey open and traced the schematic.
The sender end looked like a 3/4 turn variable resistor with distinct steps, with the wiper of the potentiometer hooked up to an arm/float. The receiver end was more complicated, located in the dash display panel, and had an Analog-to-digital converter (ADC) on it. A little thought on What Could Possibly Go Wrong, and a little fooling around with an ohmmeter when the dash gauge was showing empty (when it wasn't), convinced me that the problem was in the dash. ADC's famously have lots of comparators inside hooked up to a resistor divider chain built into the silicon. If the chain gets busted somewhere.... This was a new car, so having an ADC fail a month or so after being built is what warranties are all about. (Technical term, no kidding: Infant mortality.)
I gave my suspicions to the service desk: They, of course, took the easy way out, replaced the sender, and put in a full tank of gas. Which of course killed the problem for the next hundred and fifty miles, at which point it came back (intermittently, as before) again. I brought the car back and said some pithy things on the subject: The only other choice, for these guys, was to replace the whole dash instrument panel, speedometer, tach, gauges, odometer, and all. That did the trick and I had a sticker in the car stating that the odometer was off by the amount that was on the thing when the instrument panel was replaced.
We don't want to talk about the fact that in the process of replacing the sender they tore the gasket on the top of the gas tank, leading to puddles of gas on the ground, leading to emergency (under warranty) repair, and a mad search across the eastern half of the US for a new sender by the (better) dealer up in Boston...
Anyway: If Toyota thinks that calibrating the gas gauge is a good thing, far be it from me to argue. However, going abruptly from 1/4 tank to zero doesn't sound like a calibration problem: It sounds like something broken. Senders (in the gas tank) could fail, I guess: Pulling it out in a well-ventilated place (no idea on how to do that in a Prius; on an Odyssey, I had the repair manual, and it wasn't hard), cleaning it off, and working it back and forth with an ohmmeter checking the resistance variation will tell you if the problem is at that end. If it's not (50-50 flip of the coin from me), then it's the receiver, which is likely in whatever controls the electronics on the dash. Like I said: Probably an ADC to a computer, and the computer drives the dash display. And it's probably the ADC that's bad, if anything, at least based upon my experience.
Finally: My old Avionics Chief Petty Office stated that, "90% of your problems are going to be in the wires." I found that philosophy to be dead on. Corrosion, bad connectors, flaky wires, broken wires, etc. are always there. This is why one has repair manuals: If the fault is present, running about with a voltmeter and ohmmeter can dig out the Reason Why pretty quickly.

KBeck.

 

This comes from the Gen 2 fuel bladder. You had to put 4-5 gallons of fuel to get the "guess gauge" to recognize any fuel was added. If you added less fuel, your guess gauge would continue to count down from where it was and would not register the new gas you just added. Thus your gauge did not accurately tell you how much fuel was actually in the bladder. You had to wait until enough burned off to be able to add greater than 4-5 gallons before the guess gauge would "re-calibrate" Thankfully, they fixed it in Gen 3 and newer.