1998 Silverado Z71 Service Engine Code Help

1998 Silverado Z71 has the service engine soon light on. Here is what the code is reading, PO420 - Catalyst Efficiency Below Threshold. What does this mean & how do I fix it?

Same code here, does anyone know the most common fix for this? I am trying to avoid buying the convertor

the O2 sensors are in need of replacement if over 100,ooomi.........
If after replacing the O2's you still have the code you will need new cats....

you could try soaking the cats in an acid bath,this may get the cat to work longer...acid will clean the metal interior...

to soak these you will need to remove and soak for an hour ..20% acid water mix..

http://www.automotiveforums.com/vbulletin/showthread.php?t=622469

replace gas cap with vented one and blow system with a can of seafoam. i think, i fixed 6 or 7 CE lights on various cars like this so far. including my 00 silvie.