P0139 code on Hyundai V6 Sonata?

Now you have to inspect wiring and scan tool data to find if ithe o2 sensor is working correctly.

Thanks let me take it to mechanic who changed the O2 sensor to inspect the wiring & scan tool data ,tell me one thin how many O2 downstream sensors are there ? My mechanic said with one sensor hopefully both the error code P0139 & 0137 will go whereas when i google it mention there are 2 O2 downstream sensors. Pl advise accordingly?

one code P0137 is gone whereas P0139 is still showing.

It depends on the system. V6 and V8s usually have 4 o2 sensors all together and 4 cylinders usually have 2 sensors. Bank 1, Sensor 2 is the one your code is correlating with. Which Sensor 2 is behind the catalytic converter often called a downstream. Bank 1 is off whatever side of the cylinder head cylinder 1 is on.