o2 sensor
 

hey guys, i'm new here and i'm trying to get my mother's check engine light to come of on her 1998 quest. I hooked it up to an OBDII machine and it reads O2sensor circuit malfunction. I've replaced the O2 sensor and reset the codes and the light will not go off. I've replaced the fuel and air filter hoping to make the emissions better but that still didn't work. I don't know what else to do and it won't pass inspection with the MIL on, anyone know what might be going on? Any help is apprecitaed, thanks

RE: o2 sensor
 

did you replace the right o2 sensor? did you use nissan parts or aftermarket? Todd