GM has been using these RPO codes for years and a few more
FHO Vehicle Fuel Gasoline E10
FHS Vehicle Fuel - Gasoline E85


One thing to remember the PCM uses the O2 sensor as a tool. The PCM drive the O2 sensor voltage to a set parameter and the drives it back the other way. The PCM drives the O2's with the injectors. Try swapping the O2 leads from side to side and then think about it. You will find the engine will surge and the fuel trims will not be the same. If the O2 sensor is mounted too far away the PCM will get out of sync because of the added duration it takes for the PCM to see the target voltage