I recently installeda MAC offroad prochamber h pipe.. 2 weeks after that, i put on the BBK mil eliminator wire kit. I disconnected the battery and no engine light was on. A week later the light comes on and i got 2 codes.
P0156- Downstream Heated O2 sensor circuit fault, bank 2.
P0420- Cat. efficiency below limit, bank 1.

I need help with this.. Do I have a bad O2 sensor and/or is the mil eliminator kit no good? Or is it something else? Please let me know what i should do!