what code will you get with failed oxygen censors? on 1996 Toyota Land Cruiser

my check engine light is on and i thought maybe i will change the o2 censores first opose to changing the convertors.

Asked by for the 1996 Toyota Land Cruiser
P0420 is a cat converter below efficiency.
All codes around P0130 are O2 related coeds.The front O2 sensor should give a fluctuating voltage at say 2000 RPM at the same time the rear would want to be relatively flat line if the cat is OK but you need to compare the readings using a two channel oscilloscope.
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What are the trouble codes.
i think it was p240 , and another ralating to the egr system.
There's no such trouble for this vehicle. Getting the exact and all codes will assist in helping you.