When the battery dies or has been disconnected it activates the anti-theft system for the radio. Here are some steps to help you out.
1. Look in or on the side of glove box for small sticker with numbers, should be 5 digits with numbers no greater then 6.
2. Pull out the ashtray and see if the sticker is on the back of there.(older models that have them)
3. If you turn off radio and hold the 1 and 6 preset buttons then turn radio on it will give you the serial number. They will ask verifying questions. You may have to pull radio from dash and write down radio serial number and call local dealer with that number and they will be able to get the code for you.
4. If you happen to have all the books from the dealer look in the 'HONDA SERVICE HISTORY' book, NOT the owners manual. It should be on the first page in the AUDIO CODE box.
You can go to this site https://radio-navicode.honda.com/ but you will have to prove you own the car. Honda knows if the dealer that you bought it from reported it to them.
