Generally on the newer engines the front O2 sensor needs to be close or at the crossover ( "Y" pipe) and yes you have two of them. One at the crossover and one after the catalytic converter. Just to let you know the one after the cat will not set an O2 code. It is used to check the cat.
When they moved the O2 on the exhaust, Did they use a new one or the original one?
If they moved it lower, Did they have to lengthen the wires? Sometimes splices (depending on which kind they used) in the wires could affect the O2 sensors readings.
i think i understood what you were meaning here, but its just a lil unclear and for the sake of this thread... just clarifying, the rear O2 will set the check engine light off, but the code will be something related to the cat...
My back o2 I found is unplugged. I dont understand why. Also I do not have a cat. The o2s are stock and I never changed them. I have to got to emmissions soon so my 02s are suppose to be tuned out so why would I get a light??
if you dont have a cat... you dont need the back o2 to be plugged in if the codes are turned off in your computer.
the rear o2 is primarily related to the catalytic converter, which the codes are related to, the code your car is setting is the front o2 code... those codes should not be deleted from your computer, if i were in your case, i would replace the front o2 sensor. especially since you reported it to be "stock"...