"E23 Communication Error: There is a vehicle/radio communication problem or an inter-radio communication problem. Disconnect battery voltage to the radio and then reconnect*after a few minutes."
If it still doesn't work after that, go look for a replacement on eBay (under $100... yes I know there's aftermarket, but I personally prefer the OEM look and the steering wheel radio controls. Besides, I have the Bose in mine, and switching to a third-party system would involve a lot of work...)
--Robert