Try code 1111. See additional details below.
Radio Security Code (1999 Kia Credos)
When the car battery is disconnected, the radio read out will begin to flash for a while. Then, “CODE” will be displayed. At this point, you can.enter the security code. If code not entered using instructions below, the radio will cease to function properly; and you will have to power the radio off; and wait for “CODE” to be displayed again. Following are instructions for entering that code:
Code is 1111. However, to enter 1111, you actually have to
1. Press the 1 button, then a “1” will be displayed.
2. Press the 2 button, then the second “1” will be displayed.
3. Press the 3 button, then the third “1” will be displayed.
4. Press the 4 button, then the fourth “1” will be displayed.
Then, press the volume control button, and your radio will begin to work properly again.
David, January 2010