MIL Question

I have a 1996 Mustang GT and have cut 4 of the 6 catalytic converters off of the exhaust. I put on a set of MIL eliminators when I did this, but have recently started getting a check engine light that comes on for a while and then goes off again. I went to Auto Zone the other day and the codes show the O2 sensor on bank 1 sensor 2 which would be the O2 sensor aft of the cats on the passenger side.

Question is this...Do I have a bad MIL eliminator or should I go ahead and replace the O2 sensor?

Car is not running odd when the light comes on or anything, the light just bugs the crap out of me!
 
I would check the mil eliminator wiring (or plug in depending on style you bought) and verify that something hasn't worked itself loose. What exactly IS the code? Some codes refer to the sensor readings - emission wise, and some codes refer to the sensor itself being bad.