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Have the very common P0420 scan on the new Impala I bought. I'd appreciate it if some of you had a look at this scan with HPT and give me an educated opinion on the cause of the problem. I added the downstream O2 sensor to the main table so both O2 sensors would be logged.

Car is a 2004 Impala LS (N/A 3800SII)

The huge KR spike at WOT might be from having a bad motor mount plus a dogbone mount that's cracked in two. Motor moves around more than it should.


Thanks in advance.