Help with P2238 code / O2 sensor?

I recently had a mechanic swap out the motor in my 2013 Prius (the previous one had a blown head gasket). I thought that the swap went well as I have already driven 1000 miles with no noticeable issues. However, the check engine light is on with code P2238: O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 1

The check engine light was on when I received the car back from the mechanic, but I assumed it was still on from the misfiring due to blown head gasket, and he just didn't take the time to clear it. Is the O2 sensor thing a common issue to get triggered after something like a motor swap? Does it seem likely that it is a serious issue to have looked at? What would the symptoms be?

I know I need to just take it back to the mechanic to inquire, but English is not his native language, so he is pretty hard to communicate with. I just wanted to get a read on this forum. Thank you,