How do I know if the o2 senser that's bad is the upstream or downstream?

Question

The code said I need to replace the oxygen senser, how do can I tell which one?

Answer 1

HI there,

The code is usually specific to the sensor, for example HO2 B1 sensor 1 would be the heated O2 sensor on bank 1 and sensor 1 which is before the converter. If the code doesn't give you a specific location, then you need a scan tool that can read the info coming from the sensor when it's running to determine which sensor isn't working properly.