what causes a something to run rich? Leaking injector (but not likely), spark plug not firing (your Rinda will tell you ignition miss per cylinder, may just have a corroded terminal guess how I know..). The precast O2 sensor never go bad, the post cat sensors are exposed to water and exhaust gases and my failed every 18 months till I removed O2 sensors permanently (CP Performance O2 simulator) also removed cats. All your sensors are to protect the precious catalytic converter.
Is this a ghost code or does it come back. You need to go into history on your Rinda and clear codes there, just clearing without clearing history doesn't clear from PCM. What your history say on your Rinda? At what speed and temperature did alarm occur? It shows the engine conditions when code was set. You need to spend some time with your Rinda its a lot more than a code reader. This may have been a one time ghost code, ask how I know that....