You dont mention which code in particular but since you said its running lean im fairly confident its talking about one of the upstream O2 sensors. If thats the case you cannot put O2 simulators on those as those wouldnt tell the PCM correctly how to adjust the fuel. The upstream O2s are in the exhaust header and those should stay as is and correct the issue at hand.
O2 simulators are meant for downstream (after catalytic converters) only. Its for folks that run "offroad only" and dont have any cats.
I agree with flatline there a bit, need to first see whats going on, if you got access to a live scanner, would like to see what the o2s are reading and how they are switching back and forth. Lean represents its sitting more on the 0.7-0.9v side instead of around the .4-.5v side (which is where it should be for correct a/f ratio). But the live chart will show it switching up and down evenly. If it leans more on one side then thats where it determines if its running lean or rich.