Lexus / Toyota help 2jz

[Papa_Jon]

I have a 1998 gs300 throwing 420 code bank 1 below threshold, As i check o2s it shows all them have same volts, only thing i see different is bank 1 senor 1 shows no movement .
would a upstream sensor cause a 420 code?

 

[Wwildman]

The P0420 code is set by the down stream o2 sensor when the two sensors have matched voltage for a certain period of time. you can put a after cat O2 in it and it might help but if the cat is bad. well it might need a cat

 

[Papa_Jon]

Upstream 02 is shOwing good volts but no 0in fuel trim. Rest are Moving and adjusting