DTC P0138: Heated Oxygen Sensor Circuit High Voltage [SEMSOR

i pulled this code out from my obd2 scanner. anyone have any ideas on what this could be?
im thinking it might be the o2 sensor on my test pipe. anyone know what number o2 sensor is on the cat area?
its been raining CRAZY here in so cali so i'm thinking possibly that the o2 sensor on my test pipe got wet or the wires got shorted.

anyone have any thoughtS?