Filling the tank takes Forever!

Oct. 2009 - check engine light came on & tank accepted .5 gallons at a time. Caddy mechanics replaced the carbon evap canister, swapped filter and cover. July 2010 - repeat of above problem so on Aug.2- replaced the evap canister and vent again. 2 days after this repair, check engine light is on but can fill the tank just fine. Caddy replaces the gas fill cap because the old one doesn’t click when putting it on. Caddy mechanics offer to replace the metal neck for $371 - but this we decline as we have driven several vehicles and never heard of a reason to replace the gas fill neck. Problem seems to be ok after the new fill cap…until 3 weeks later check engine light is on again and now accepts an average of 3-4 gallons at a time before nozzle shuts off. Takes about 45 seconds per gallon to fill and it’s not ok!

Are you in the habit of topping off the tank when you get gas? If so that could be the reason. If you look around in the owner’s manual and at the labels on your car, you likely will find that they warn agains topping off the tank. It can cause this kind of problem.

In any case, I am going to guess it is a problem with that vent system. I believe you need to find a mechanic that knows what they are doing.

BTW could you give us the actual error code? It will be in the format [P0123]

Here’s what I found on invoices:
Aug 10 - error code P0446 eval perform and P0451 FTP sensor, perform evap purge/seal test - failed, will not exhaust fuel tank pressure. Comman…vent solenoid on/off seveal times with tech2 to get valve to open and release fuel tank vacuum. P/A vent solenoid and evap canister.

Oct 09 - error code P0420 Cat.converter efficiency and code P0451 fuel tank pressure sensor

Your gas tank is not venting correctly. Since you have already had work done with dealer mechanics, make sure it is their fault. It is.
The pumps you are encountering believe the gas tank is full after every five or ten seconds filling. It is just not your fault, and even if it not Caddy’s fault, they should do more to help their customers but to offer meaningless replacements of the metal neck (???) for $371. The problem is the car. By design. Make them fix it.

Thank you so very much for looking this over. I am usually hesitant to insist on repairs, especially since I don’t have a background in this area. A very good week to you, and again, thanks!