From the page titled "Radio Theft Protection" in my 2008 owners manual."Your vehicle's audio system will disable itself if it is disconnected from electrical power for any reason. To make it work again, you must enter a specific five-digit code in the preset buttons. ...You should have received a card that lists your audio system's code and serial numbers. ...If you lose the card, you must obtain the code number from a dealer. To do this, you will need the system's serial number.If your vehicle's battery is disconnected or goes dead, or the radio fuse is removed, the audio system will disable itself. Use the preset buttons to enter the five digit code. ... When it is entered correctly, the radio will start playing.If you make a mistake entering the code, do not start over; complete the five digit sequence, then enter the correct code. If you are unsuccessful in 10 attempts, you must leave the system on for 1 hour before trying again."(If you have a navigation system the code is four digits instead of five digits.)With my vehicle I got a booklet titled "2008 Honda Service History." On the first page of that booklet is the audio code. (It also has the "key code" which you want to make sure you keep in your records in case you ever want a spare key made.)