i have a 97 blazer and about a month ago my ses light came on and i had a bad cat conv i recently replaced it and the light turned of but about 3 days ago my ses light came back on so i took it by auto zone and had them run a test on is and it read that i had a bad converter so does anyone have any idea about whats going on

 

Quite possible that the converter was never bad, but the O2 sensor behind or in front of the converter is bad. What is the specific code?