How can I know wish of the Oxigen sensor is the one not working?

Question

I need to change the sensor but it has. Like.  2 top  and 3 bottom

Answer 1

The oxygen sensor , the ones on the top are known as the upstream or engine management sensor it is listed as Sensor 1, The down stream oxygen sensor is right after the catalytic convertor this is known as the downstream 02 sensor or catalytic monitor sensor which monitor the catalytic threshold, These are known as Sensor 2.So if you set a 02 sensor code it would be something like Bank 1 Sensor 1 which mean the upstream sensor at the number one cylinder, Another code would be Bank 1 Sensor 2, which is where cylinder 1 is located and Sensor 2, which is the downstream 02 sensor which is after the catalytic convertor.