In a Nutshell... I haven’t been able to fill the tank over ½ full for at least 3-4 years.
I did the usual search and checked fuse E6, nope, that wasn't the problem.
Then I was told it was maybe a blocked flap from slipped tubes in the tank. I went through that scenario as well. (Which by the way is not for post 2000 models, I found that out later) I removed the fuel filler tube, fuel sender and fuel pump... inspected everything etc. Everything was fine!
Now what?
I started to take all the check valves apart to inspect... The charcoal canister etc... again, it all looked and worked fine. I was stumped. Next step was to check continuity of all the electronically controlled vent valve wires and to see if the valves themselves even worked independently. At this point I enlisted the help of my father-In-Law. He's an electrician by trade and a shade tree mechanic. All the valves worked when we gave them direct power to the battery.
So we studied the wire diagram for the ORVR system... then started to splice wires.
This is how the tank vent is supposed to work:
Gas nozzle goes in, hits flapper, flapper opens magnetic "reed" switch that is mounted to the outside of the filler tube, the reed switch tells two electric valves to open. One valve is on the tank (under battery to the right) and the other is in a box in the front right tire well (between tire and bumper). This whole process opens venting to allow the tank to fill.
My problem was that wherever the reed switch was engaged the signal was shorting out and not bringing enough volts back to activate the vent valves. Somewhere deep in the firewall there’s a terminal that ties these all together. That connection was either loose or corroded and was taking all the voltage from the ORVR system but not blowing a fuse. We ended up cutting that terminal out of the equation by running a direct wire from the vent valves to the reed switch! Everything works perfect now!
This took longer than anything I've ever fixed on a car, and I've done a LOT. My timing belt on my Audi may have been a little harder though
I know it sounds confusing... I still have a hard time understanding, but thankfully I can fill the tank now