Most car stereos come equipped with an antitheft radio code. The antitheft function activates if the battery is disconnected from the vehicle, if the battery dies and if the radio is removed or disconnected from its harness in the car. You will need to enter the antitheft code into your radio in order for it to resume functioning. If your car radio is locked, there are simple steps that you can take to unlock it.
Locate the antitheft/unlock code. Most cars have a special antitheft radio card that is included with the owners manual packet containing the unlock code and serial number. Some cars also have the code in the car manual or inside the glove compartment. You will need this code in order to unlock your car radio.
Turn the car's ignition switch to the "on" position. This turns on your car's electrical system and powers up the radio. The word "CODE" will display on the screen. Note: depending on the manufacturer some radios will display either "ENTER" or "LOC" on the screen instead.
Enter the antitheft/unlock radio code. Press the "Tune" button on your stereo. It will change the screen from "CODE" to blank. Press the button to scroll through the available numbers. When you reach the correct number press the button once and hold it down for a few seconds. The number will appear on the display and you can now repeat the process to input the second number, third number etc., until all of the numbers are in. If you entered the code correctly the car stereo will unlock and instantly become functional. Depending on your car manufacturer, if you enter the code incorrectly you will not be able to re-enter it again from 1 to 24 hours.
Call your car manufacturer directly. Your car manufacturer's phone number is in your owner's manual. Ask to be connected to the support department. Tell them you need to reactivate you car stereo and you will be asked for proof of ownership. They will need your car's VIN number, the account number from your bill of sale and a form of personally identifiable information like your driver's license. You may need to fax this information. Once everything checks out the manufacturer will give you the code.
Enter the code and unlock your stereo. Use the code you received from the manufacturer to unlock and activate your car stereo.
Go to a car dealership. Take your car to its manufacturer dealership to get the stereo unlocked. For example, if your car is a Honda go to a Honda dealership. Once you have proven that you are the owner of the car, the dealership will be able to retrieve the code from the manufacturer and activate the radio for you.