A dead battery in a Honda Civic causes multiple problems. It prevents the engine from starting, and it also could prevent your car radio from working properly even after the battery gets replaced or recharged. This problem develops only with car radios that are equipped with a theft-deterrent system. Resetting the radio is a fairly simple process, provided you have the device's unique identifying code on hand. If you don't, fixing the radio will take a little more time and effort.
Verify the problem exists
Confirm that your Honda Civic radio is equipped with a theft-deterrent device that will require you to punch in a special code with four or five digits. The code will disable the device, which is meant to stop thieves from operating an audio system they have stolen. If your car's audio system has a theft-deterrent system, you will see an electronic message on the radio once the car battery is working again. The message could be the word "CODE."
Find the document with the code number
Locate a document that displays the four- or five-digit code number needed to unlock your Honda Civic radio. You should have received this document when you bought the Civic and got the owner's manual for it. The document could be roughly the size of a credit card. It also should display the serial number for the audio system.
Locate a lost code number
If you cannot find the code number, you should try instead to find the audio system's serial number because this will help you to track down the radio code. Some newer Hondas allow you to obtain the serial number electronically from the radio, but you need to consult the owner's manual to learn how to do that. When you have the serial number, you can then get the proper radio code by going online to the Honda Radio & Navigation System micro-site. The micro-site will require you to provide the car's vehicle identification number and other information to prove you are the owner.
Ask a Honda dealer to help
You may need to seek help from a Honda dealer if you continue to have difficulty, especially if you are trying to get the serial number for the radio in a Honda Civic made in 2003 or earlier. The dealer, who likely will ask for proof that you are the owner of the Civic, will be able to track down the radio's code number.
Punch in the code
When you find the code number, use the preset buttons on the radio to punch in the proper digits. This will reset the radio, disable the theft-deterrent device, and enable you to resume listening to music in your Civic. If you accidentally make a mistake while punching in the digits, you cannot backtrack. Instead, you must finish entering the proper number of digits, even if they are the wrong digits. Then start over again and try to enter the correct code. Be aware that repeatedly entering the wrong code within a short period of time will trigger a lockout mechanism on the audio system. You must leave the system on and undisturbed for at least one hour before you can make another attempt.