Engine knock when fuel indicator flashing low

I'm guessing your engine had a misfire, which may not have been enough to light up the Check Engine Light (or possibly it did, but you have not said anything about that). It's not good to let any car get down to the last bit of gas in the tank, the reason being that any water or other impurities settle to the bottom of the tank and will be sucked up by the fuel pump when the tank is almost empty. I would guess there was just enough water in your tank to make the car hesitate momentarily, but not completely stall. It is especially unwise to let a Prius run low on gas, given the temptation many succumb to when running out of gas, to try to make it to the next gas station on battery power alone, thus draining the HV battery to the point where it can no longer start the engine. There have been members on this forum who have purposely run out of gas in their Prii, to document what the true range of the car is, but they have generally carried extra gasoline with them in a container, to keep from being stranded, and I expect these were relatively new cars that had not had the chance to accumulate impurities in their gas tanks. It should be noted, however, that some of us do have a certain gene in our genome (I believe that's the way one member described it) that pushes us live on the edge when it comes to keeping enough gas in our tanks. Probably those who suffer from this malady have another explanation for this behavior, but I believe the impulse should be resisted, no matter what is behind it.

 

This is very true, but tangentially related.

In North America, the Gen2 has a flexible bladder in the fuel tank. It will never hold 11.9 gallons but will hold variable amounts depending on outside air temperature. I have had 10.5 gallons at 105 degrees F and 7.5 at 20 Degrees F.

As such, you never know how much fuel you have left. I have run out within 8 miles of the blinking starting. Other times it goes 40 miles.

My advice, worth all you paid for it.
If your mother in law is in the car, get gas when you still have 3 pips.
If you spouse is in the car, get gas with 2 pips.
If you are driving alone get gas with one pip.
If it ever starts blinking, GET GAS NOW!

If you let it run out of gas, do not try to start it until you put at least 3 gallons in it. If you do, it trips a code the dealer can reset when it is towed to him.

YMMV

 

The tank might actually be lower than you (or the gauge) thinks it is......and you are about to run out of gas.
OR
When the fuel gets real low like that, some "contamination" in the bottom of the tank gets sucked in.

A healthy dose of a good "all purpose" fuel system cleaner might help.
Might not too but certainly shouldn't hurt.

 

PATIENT: Doctor, it hurts when I do this.
DOCTOR: Then don't do that.

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