i have a 2000 Chevy Monte SS 3.8, I recently went to get my check engine light on and it said I needed a new bank 1 sensor 1 replaced and I did so. I need it fixed to pass emissions. Well I replaced it and the light was gone, then two days of me driving the car back and forth from work it came back on. And had it check and it's the same code for the sensor. Is there two bank 1 sensor 1 and where is it located I changed the one In the engine

 

There is no o2 sensor in the engine. They are all in the exhaust...

 

Bank 1 sensor 1 is upstream from the cat.

 

Would you remember the brand name of the replacement sensor? Seems like I remember reading the Bosch were not the best for our cars. Denso or the A/C Delco tended to be less problematic. Perhaps the sensor you bought is not ultimately not compatible with your car.