need help with ses light

[my02denali]

i have got a P0420 code on my 02 silverado-5.3 engine.has anyone had this code and if so what fixed it

[mnstrmdnss]

a P0420 says your pcm indicates low cat efficiency on bank 1. could indicate an exhaust manifold leak at the head or donut connecting the dowpipe to the manifold. could mean a lot of things, but in the case your truck is so new, most likely its your o2 sensors pooped out early.