BOLAS

I have the obd code P0128 and P1133 in my 2001 accent..
I need someone to tell me what kind of troubleshooting do with these codes,
I have the scanner but i need a program or somebody that can help me with the
definition of the codes.

In the P0128 code it says that the temperature is too low. I change the
termostat and the light came back again in a couple of days, im thinking of
changing the coolant sensor. Everything is ok, the fan is working , the
coolant fluid is new and the temperature is good also.
Any other thing that you guys think could be?

In the P1133 code it says something about the oxygen sensor, Maybe it needs
to be replaced?

Any help would be great ,thanks.