The radio code for a Honda Civic EX is a private, anti-theft serial number located on the identification card that is sold with the car. A unique number is assigned for each vehicle.
If the radio code is not with the manual that came with the Civic, it may be inscribed on the control unit. The exact location of the control unit varies with the car, and is located in the Navigation System booklet. If this search proves unsuccessful, the radio code can be found by turning the ignition on, waiting for it to read "CODE," then turning it off. Next, hold the one and six preset buttons, then turn the ignition back on. The eight numbers that show up on two successive screens form the radio code.