Engine is throwing this code:

P0138 Secondary Heated Oxygen Sensor (Secondary HO2S) Circuit High Voltage

from what i understand there are two O2 sensors. Which one is this one and where is it located? Also where can i get a replacement one that is plug and play thanks.

Sorry if this topic has been covered before.

 

The secondary o2 sensor is the one attached to the end of the cat, autozone or anything like that or OEM

 

thanks for the info.