if whatever scanner you are using doesnt tell you which sensor has an issue then get a different scanner it should say for example P0xxx whatever the code is then say for example HO2S Heater circuit High/Low sensor 2 which is the rear sensor. The rear sensor is basically useless it just compares data with the front sensor however if the front sensor goes you will definetly notice because your car will run like a pile of dung because the ecm receives a bad signal or no signal at all screws of the fuel trim data and makes the engine buck the a spurred mule
