Mitsubishi Repair: Check engine light, o2 sensors, o2 sensor

Question
I had my o2 sesor replaced and my check engine light keeps coming back on. The only code that shows up is the o2 sensor.... what gives? Also I have noticed a big drop in MPG

Answer
Yolando,
Most cars (made after 1994) have two O2 sensors.  You should ask your mechanic if both were changed.  Also, if your catalytic converter is not working properly, it can put extra strain on the O2 sensors, and can cause your check engine light to come on.
Good luck!