I have a 00 z28 it keeps throwing a check engine light code.0420 catalyst efficiency below threshold (bank 1). I replaced both oxygen senors on that side, I went and had the code cleared and bout after 150 miles it has came back on. I went and had it checked today and it was this same code again?? The only other thing it could be is the cats i think?? I know i am going to need the o2 simulators, and where is the best place to get them?? I am gonna go tommorrow and see bout cuttin them off, if i go ahead and cut them off without the simulators will may car run okay? I know the check engine light will be on for sure. Thanks guys for all ur replys.

 

The car will run fine without the cats and the SES on until you get the sims.

SES for rear O2 has no ill effects.