2001 Toyota Tacoma PO420, CALIFORNIA EMISSIONS

I HAVE A SES LIGHT, CODE PO420, CHILTON BOOK IS NOT VERY SPECIFIC ABOUT O2 SENSOR READINGS, BOOK SAYS THE O2 SHOULD READ BETWEEN .1 AND.9V, IT DOES NOT SPECIFY UPSTREAM OR DOWNSTREAM. ON MY TRUCK, THE UPSTREAM SENSOR IS READING APROX. 3V AND THE OTHER ONE IS WITHIN THE SPEC IN THE BOOK. THE TRUCK IS CALIFORNIA EMMISIONS AND I DONT KNOW IF THAT MAKES ANY DIFFERENCE IN WHAT THE READINGS SHOULD BE.
ALSO, I REMOVED THE CAT. CONVERTERS AND LOOKED INSIDE TO SEE IF THEY LOOKED BAD OR CLOGGED AND THEY BOTH LOOK CLEAN, ALMOST TOO CLEAN, NICE AND WHITE.
I WOULD APRICIATE ANY HELP BECAUSE ALL OF THESE PARTS ARE WAY TOO EXPENSIVE TO GUESS ON