As a security feature for a car radio to deter theft and use of the radio in case it is removed or detached from the vehicle or if by some situation that the battery is disconnected, you will need to input the code specific for the radio in order for it to work again.
And even if the serial and model number of the stereo is obtained, for the code to be unlocked as well from the manufacturer, this will still need the VIN of the vehicle for the code to be provided and be used so that the radio will be functional again.
In obtaining the code, you will have more than one option, and how it is obtained also depends on complexity and cost, that if you are in a situation where such predicament have to be addressed.
You may have the option to check the user’s manual, check the OEM’s website, call your local dealer, search through free online databases and they will need info. like the make, model, year, and VIN of your vehicle together with the serial and model of the radio, but this is somehow a courtesy service that they are not obliged to provide.
In the event that none of those mentioned above are accessible, you will have the final option of paying a local shop or online service to locate or calculate the code, and these services are paid and they are able to generate and provide radio codes of almost all car manufacturers with the use of the serial number of your radio.
When this is your first time to input a code for your car radio, make sure that you know the procedure or operation of the radio device on how to correctly code in the needed code, otherwise, you will be locked out if you put in the incorrect code several times, and you will have to reset the radio and wait for an hour or so depending on the type of radio, before you can access the point where you can input the code again.
Just accessing the code may be a daunting task, therefore if you happen to have that code, keep it safe or noted safely where you can have direct access to it personally, so that you will not have to undergo the same trouble again should it recur, and you will not be paying again for the code in case it was bought online, however there are some online services that offer free radio code recovery for your code that was previously ordered from them, so you need not pay again for the same code.