P0128 thermostat code for 2002 Ford Focus with 2.0L engine

Question:

This engine has a P0128 code-coolant temperature setting below thermostat-regulated parameter; engine rpm is rough every time the light is on. Do I have to change the thermostat on this?

Code Description:
This code is very common on this engine if the thermostat is stuck or partially stuck open. To check make sure the radiator cap is good or replace it if possible. If the light still shows up, replace the thermostat.

Repair Tip:

After replacing the thermostat, make sure to reset the engine code. Should the code returns, contact ATS for further assistance.