2010 Prius gas tank won’t fill

Hi!
Bought a new-to-me 2010 Prius III a few weeks ago. It has about 174k miles and has been running really well.
It has problems filling the gas tank though. I’ve tried a few different stations but I can’t put more than about 1/4 gallon in at a time without the shut off clicking. I’ve tried pulling it out some, turning it sideways (both directions). I can hear the sound of the air change like the gas is running up the neck even though the tank is quite empty.
Thought it might be the charcoal canister assembly. I picked up a used one on eBay and installed this weekend but it didn’t help at all.
The eBay module looked great and came off a working unit but it is possible I got a dud from the seller. Could the smaller vapor canister filter be causing the problem?
Looking for any suggestions on what else it could be?

Thank you!
Tom

 

Thanks for the reply. Carfax is clean but it has been bumped in the rear before. Nothing structural looks out of sorts under the rear of the car.

I’ve got a borescope and am thinking similar to you that I need to have a look down the filler neck and also check the lines themselves for clogging.

I had quite a time getting some of the clamps off the lines. Is there a trick to releasing them?

 

I can appreciate the EGR bunny trail when folks see a newbie post about a high mileage car. I think folks just want to be helpful since a head gasket failure can be a death-blow for an older vehicle. I’ve been lurking on this site since I bought the car and the full maintenance package is on my todo list as soon as the weather warms up. I can say this oil appears to have 4K miles on it, is right at the full mark and is still a nice amber color.

I’m going to try the borescope and pull a few hoses this weekend to see if anything interesting shows up. The diagram ChapmanF provided is very helpful in showing where the potential choke points could be. Not much else besides physical restrictions now that the evap unit was replaced.

My only other thought was the little box in the bottom right of the diagram. I think that has a filter of some sort inside and will probably have to take that off for inspection as well.

 

I think I finally figured this one out.

Right at the end of the filler neck is yet another charcoal canister. It is the last stop the vent hose has before it makes it to the atmosphere (venting behind the rubber lip at the top of the filler neck). I blew a shot of compressed air through the line at the bottom of the car and was treated to a cloud of dirt from the filler neck that filled my shop so much it felt like I was in a Dukes of Hazzard episode.

At that point I decided to pull the entire filler neck and do a deep clean. After discombobulating the full line and both vent hoses I was able to extract the filler neck assembly from the car. I managed to get the charcoal filter removed from the filler neck and ran some hot water through. I got enough gravel out of the poor thing to build myself a playground.

I flushed that little bugger out for about 5 min until I got nice clean water out from both directions. Dried it all out with compressed air and reinstalled. Unfortunately my wife filled the tank yesterday so I’ll be able to test this out in about a month when it finally needs gas again!