Well, do you have power to the heater circuit on that O2 sensor?

 

This is a precise operation that has to have the exact codes and the whole system involved, checked out. What are the codes..again.
This is just ****in around!
Sorry for my precise opinion.
Any body can read what a scanners says but if they don't know what it means,, might as well throw the scanner away.

 

There are no codes that tell you a sensor is bad.

The codes are only there to tell of a condition that is out of range to the pre-set parameters in the ecm

Codes are ONLY for a diagnosis starting point NOT what sensors to replace.

You also only mention one o2 snsor. your truck should have four, two of which are primarily active. (Before the cats)

Good luck as it appears that your mechanic has no idea how to trouble shoot what caused the code. He only knows how to throw parts at it.