Got the dreaded SES after I upgraded the stock cat to a 3" Catco. Autozone read a 0420 from the O2 sim behind the cat on my 2001 Firebird. What is the problem and how can I get rid of the light?

Thanks

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2001 A4 Pewter FIREBIRD Convertible

LS1 motorsports lid, FRA, raised airbox, K&N, BMR STB, 3" Catco Cat, 3" S-pipe, 3" Borla Catback, Red-Line Water Wetter

Tinted Windows, 'bird decals on the mirrors, Pontiac Decals, Firebird Decals, Mobil 1 Oil Cap

 

You have two O2 sims right? Why didn't they just tell you what the code meant?

Unfortunately I don't know the OBD II codes.

http://www.obdii.com/codes.asp