1997 Isuzu Rodeo Question OBD2 error/trouble code, O2 sensor

Check engine light came on. Obd2 code says P1133 which when I looked it up online said "heated oxygen sensor insufficient switching. Bank 1 Sensor 1". I've been told that Bank one means before the cat. Converter, but no one seems to know if Sensor one means it's the sensor on the drivers side or passengers side exhaust pipe. My rodeo apparantly has 2 sensors before the cat, one after the cat, and one IN the cat. (Everyone i've talked to thinks there isn't supposed to be a sensor in the cat) I changed the drivers side o2 sensor and the one in the cat, but the check engine light came on again. So, is anyone absolutely positive that "Sensor 1" is the passengers side o2 sensor? Or did replacing the random o2 sensor in the cat. With an o2 sensor that's meant to be a pre-cat. Sensor mess things up?