An internal short in the O2 sensor is possible although not probable.
Simply disconnect the rear O2 sensor harness connector, wire it up out of the way, clear your DTC codes and see what codes (other than P0420) appear. If your P0041 fails to reappear, the O2 sensor needs replacement. If P0041 reappears, the O2 sensor is not the problem source.
Are you in a hatchback or a sedan?