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Angry Code 0420

2006 Impala 3.5 Flex with 162,000. Recently code appeared and I did the usual information gathering on Google, etc. Downstream O2 sensor was factory original (replaced) and thought why not the upstream (replaced that one too). Still getting code. Is the CAT the next step? Found one on Amazon and can get it installed locally for a good price. Any other recommendations?

"Nothing is impossible for the man that doesn't have to do it himself" ... Weiler's Law
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^+1. P0420= cat efficiency below threshold (bank#1 ). Bank#1 is where #1 cylinder/spark plug reside. How many cats does the eng. have? How's the driveability/power?
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