I have a 2007 G35 Journey that is still giving a P420 code after replacing the passenger cat and all 4 O2 sensors. I ran the mode 6 diagnostics on my Blue Driver OBD2 reader and it shows failure of TID:01, CID:01, TID:02, CID:02. The first test description is rich to lean threshold sensor voltage and the second is lean to rich threshold sensor voltage. I've checked data from before and after sensor replacements and there isn't any significant difference that I have found.
It does appear bank 1 is running where it should be, with voltage right around .45v, and bank 2 is running rich at .8v. I haven't checked for vacuum leaks as yet, but plan to this weekend. The car is not running any differently than at any other time in the last 6 years. Power is good. Mileage is off slightly at 22 - 23mpg. Plugs were changed about 10k miles ago, around 200,000 miles. Any insights into what I might look for would be appreciated.