I have a check engine light that has strange behavior. Last year I had a code for a bad catalyst bank 1. I replaced the catalytic converter on bank 1 and it was good to go. A few months later PO430 went off indicating bank 2 catalyst is bad. But it kept coming on and off. Eventually I noticed an odd pattern. When I fill the tank full the light will stay on until exactly half a tank and it goes off until it gets below 1/4 tank and comes back on. I fill it up and stays on until exactly half tank.

So from half tank to 1/4 tank gas I have no check engine light indicating catalytic converter bank 2. Outside of that the check engine light is on. Any ideas?