I have an offroad y-pipe installed and I am trying to turn off the engine light caused by this.. When installing the O2 sims do they replace the front or back O2 sensors.

 

the o2 sims replace the REAR o2 sensors. be sure to reconnect the front o2 sensors to their plugs (you MAY need extensions) or the car will not run right.

also, my y-pipe had holes tapped for the rear o2s anyway ( i can't imagine why) so if yours does to, you may want to just screw the rear sensors into the ports and cut the wires off just to seal the holes.

 

Or you could go to your local autoparts and buy some plugs designed for the job and not have the sensor sticking into the exhaust stream.

 

If you were maybe trying to pass a visual inspection Leaving the o2's in the y-pipe might not be such a bad idea.

 

he's right the plugs make more sense...i just stuck the sensors back in because they were there...plus i didn't know they made plugs for that...

 

Not too good for a visual inspection.

 

There's actually a GM part number for an "02 delete plug". I don't have it with me though.