Chevrolet Repair: 0420 code, oxygen sensors, s10 pickup

Question
have a 96 s10 pickup with a 0420 code. any idea what would cause it?

Answer
HI GARY,THE OLD PO420 CODE !!!THIS CODE STANDS FOR A EXHAUST CONVERTOR FAULT CONDITION ..MORE THEN LIKELY THE CONVERTOR IS LOOSING IT EFFECTIVENESS. BY THAT I MEAN IT IS WORKING BUT NOT LIKE YOUR COMPUTER [PCM] WOULD LIKE TO SEE IT WORK. THE O2 SENSORS ARE SEEING TO MUCH EMISSIONS PAST BY CAUSING THIS CODE..THIS WILL NOT HARM THE CAR UNLESS THE CONVERTOR PLUGS UP [IF THIS HAPPENS THE CAR WILL HAVE NO POWER] OR IF YOUR STATE CK'S FOR THIS AT INSP TIME..TO CORRECT MORE THEN LIKELY YOU WILL NEED TO REPLACE THE EXH CONVERTOR AND POSSIBLE OXYGEN SENSORS AS WELL...GET BACK TO ME IF YOU NEED MORE INFO,AND PLEASE WHEN YOU LEAVE THIS SITE WOULD YOU MIND RATING THIS ANSWER. THANK YOU TOM..