Rich Engine

I have 1997 Dodge Intrepid 3.5. When i was driving to my home from work, the engine light came on and i went to a car repair shop right away. The mechanic checked from the o2 sensor, fuel pump to the code reader(one with the graphs and everything). he told me the engine was rich, and a pump was torn, so he fixed it. after driving a few miles from the shop, the light turned off. but recently i remember turning the ignition key while the car was already running(the stereo was on high, not my fault). but the light came on after a while from the incident with the same codes. rich engine. when i do on off on off on off. i get 12(computer recently disconnected) and 52(o2 sensor stuck on rich). I ll appreceate any help from you guys. thnx in advance.

2. i forgot the engine is running perfectly fine, sound, smell, the way it runs. everything is the same.