1. Is your car running hot?
2. Do you know the CE Code? How many flashes.

Stand at the rear of the car. On the extreme right hand side, forward of the air box you will see 2 plastic boxes the size of a cigarette pack. Unplug them and momentarily start the car and see if both banks are operating normally.

Those white colored plastic boxes read your cat temp. If hot, they trigger a CE light. If you ignore CE and the cats get even hotter, the CE will blink and you will hear a "beeping" in the cockpit. If you still ignore CE and the cats even get hotter (dangerous now) the box sends a signal to the ecu to shut down the offending bank.

These boxes are prone to failure. There is one for each bank. I suspect you are getting a false signal from the box, or one of your cats is bad and getting very very hot. Probablly the box...