How do you know if the oxygen sensor is bad?
Generally, the onboard diagnostics will tell you when you scan the computer codes.
An oxygen sensor is bad when it is no longer performing inside a set of parameters that are designated and optimal. The oxygen operates in a very narrow window of voltage and provides feedback to the engine to adjust the air/fuel ratio to maintain performance and emissions. If the sensor is bad and returning poor data, the performance, emissions and mileage will suffer.