O2 sensor in top front of cat, no fuse on 12v models for sensor. the wire connectors for it is located above tranny below black inlet boot for air flow meter. Heater wire for O2 sensor is a Bosch 2-wire connector and actual O2 sensor signal wire is a green wire spade male - female connector.
Your 1224 code may or may not mean you have a bad O2 sensor. Since you said earlier car was hard to start and rough running you need to get it started if possible and then move air flow meter and black hose up and down and all around to see if you have air leak from a crack in hose. Also check small black hoses going to it too for loose connection as well as any other hoses going to intake.