A p0420 code on a 2003 Kia Specta LS. what does this mean?

This code refers to the catalytic converter. If any of the following codes are also present they have to be fixed prior to diagnosing the P0420 code. Codes P0030-P0032, 0036-0038, 0115, 0116, 0130-0134, 0136-0138, 0140, and/or 0170-0172. To troubleshoot the codes, a scan tool is required to read the information that is being read by the PCM. Depending on what is being displayed depends on what you do.