Toyota Prius fill-up keeps tripping the gas pump?

Hi,

short answer:

You are experiencing a difference in pressure from the gas going in and your Prius trying to control that flow and the pollution from the emissions that goes along with that flow.

This is common and it's because of two things:

1. your Prius has a specialized gas tank system that minimizes gas fume emissions

2. each gas pump is different and you will have different results using different pumps at different times of the day (even at the same station)

full answer (warning - techie content):

Your fuel system works in a certain way, and understanding why it does what it does will explain why you are having the issues you are.

1. You Prius has a hand made gas tank system which includes several components. First is the gas cap itself, which includes a sensor (next time you take it off, look inside the cap and you'll see it). This sensor detects if the fuel system is sealed and will set off the check engine light if it has not been locked down.

You have noticed that there is a rubber seal that you have to push the gas nozzle past in order to get it in. This is designed to hold as much of the gas fumes inside the tank as possible (gas fumes from tanks being refilled are actually a huge source of pollution that is not generally known).

There are a series of carbon canisters and vacuum cylinders (the vacuum cylinders look like the ones on your main home water supply lines) that are part of your gas line after that rubber gasket. I have seen one disassembled and it is a complex little bugger.

These canisters and cylinders are designed to capture as much of the gas fumes as possible. Other Toyota hybrids, such as the Highlander Hybrid, actually have buttons on the dash that need to be pressed so the gas system automatically locks itself down and traps fumes as gas is being put in. This button must be pressed again if the driver fails to put gas in within a half-hour of pressing the button the first time to reset the system.

Once the gas is in your tank, the tank itself has an inflatable bladder that rests on top of the gas itself. As the gas is used up, and the level of the gas lowers, the bladder enlarges and takes up the space that would normally be in the gas tank. The gas sloshing around as you drive mixes with the air space it the tank and creates more fumes. Remember the "pssshhhh" sound you used to hear when you took off the gas cap of an older car? That was the gas mixing in the tank and making fumes (remember what I said earlier about emissions causing big pollution?). Most manufacturers have some sort of gas tank emissions controls in place, but Toyota's hybrids are the most advanced.

So, you have a multistage system that is designed to be as environmentally friendly as possible and contributes strongly to the Prius' AT-PZEV emissions ratings. But describing a gas tank system like this is not very sexy and pretty techie, so Toyota doesn't press the issue.

This multistage system works hard to control the emissions, and in those multiple steps, it creates some serious back pressure that usually isn't a problem. Ususally.

You may hear of some Prius tanks where the tank bladder doesn't retract completely in very cold weather (freezing or below). This means the owner isn't able to get a full tank in at a fill-up. That is our trade off for lowered emissions, and my experience is maybe one Prius out of a class of 15-20 owner's will experience it.

2. Your best bet to fill your tank, no matter what vehicle, is to go when the weather is cooler and the gas tanker isn't pulling out of the station as you're pulling in.

As others have said, gas (like all liquids) does vaporize and gas fumes do have a volume that the pump will not distinguish from liquid gas.

So (extreme example) if you fill up your tank from a pump on a 90 degree day and the gas tanker just left, the gas in the underground tank will have gone in at about 90 degrees. This will give you some serious fumes and if the gas pump is inaccurate enough (all pumps just have to work within a certain range, not be completely accurate), then you will get a lot of fumes and not all liquid gas.

And because each gas pump will be different from the ones around it (and from station to station), some gas nozzles will be most sensitive to the pressure of the Prius specialized tank and shut off prematurely.

The only things to do are to use a different pump/station next time or to pull back on the nozzle and reinsert it to try and overcome some of the pressure.

Good luck.

I use to pump gas and every vehicle is different but when any gas hit the nozzle the pump will shut off so you need it out as far as safely possible especially if trying to fill up fast.

Keep in mind that under certain temperatures when pumping gas and using the full trigger that you mainly get gas fumes and are getting ripped off. Some gas companies you'll find when certain temperatures out side the pump won't allow you to pump too fast thus saving you the gas fumes and saving you from thinking you've really filled the tank up with gas not fumes lol

Another trick is bumping the vehicle just before you try adding more fuel and that helps settle the gas and fumes.

Hope that helps and best of luck

I just held back the rubber part like filling a gas can and was able to fill the tank. Things have change now not only 50 plus year old woman are driving prius's but the men and youth are enjoying the great mileage. My Volt is a lot quieter;

Prius C Gas Tank

Do not put whole nozzle in as you would not do on any car as there is no room for air to get in and gas will not go in tank fast enough.

**** THIS BULL **** WE SHOULDN'T HAVE TO DO THIS, TOYOTA HAS TO FIX THIS ******* PROBLEM, NOR MY '89 HONDA, '68 MUSTANG, '99 RODEO OR MY '01 HONDA DOES THIS....THIS IS ******* BULLSHIT FIX IT TOYOTA!!!......IF I DON'T FIND A FIX FOR THIS IN MY '13 PRIUS C IS GOING BACK TO THE DEALER!!!!!!!!!!!!

try pulling the nossel out an inch or two.