oxygen sensor trouble

[vin_13]

Hi! I need some information regarding my O2 sensor. I have a 1998 nissan 200sx with aftermarket header and muffler and my check engine light is on. The code claims the second O2 sensor is bad. I would like to know how many O2 sensors are on this car and where they are located. My car has one sensor in the header and another after the catalytic converter with a long harness. I am not sure if this was moved as there is an adapter for a pre-cat sensor. I need to know where the second sensor should be so that I can buy one and get it replaced. Thanks!

[simounj]

The 2nd o2 sensor is the one right after the first o2 sensor on the headers. It should have 3 wires going into it.

[Waltz]

... 2nd 02 sensor is the one on the cat converter , and it will make check engine like light up if too much gaz is passing throught the cat converter or if it sense's that the 02 sensor itself is getting "lazy" so either your polluting a whole lot or your o2 sensor is done , bad gaz mileage could be an indication of unburnt gaz passing trought exaust headers
best of luck bub