I have a 2008 Pontiac Grand Prix. I had a code P071 I replace the 02 upstream and now I have P0420 I have read many forums about this issue and it seems like a common problem for this vehicle ... know has a firm answer to what can fix this issue. Help please

  • Welcome to Motor Vehicle Maintenance & Repair! Curious why you didn't change out the downstream O2 when you did the upstream? Jun 9 '19 at 17:32
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    Also, what is the exact code for the first code ... P071 is not a code as it needs to be five characters long (like the P0420). Jun 9 '19 at 17:41

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