oxygen sensor

i have found out that the oxygen sensor in my car is bad by the blinking codes but what i just found out is that there is two oxygen sensors and now i dont know which one is messed up....is there any way to know right off the bat which one or do i need to test both?

assuming you dont have true dual exhaust there is not much you can do short of pulling them both out and testing them. If you do have dual exhaust, and the sensor is messed up, one side might smell more rich than the other.