Hi,the thermostat is not to expensive to replace,I do like to use the dealer parts when possible. I would like to know what the temperature was before just replacing parts. If they say it read 195 there is no reason for the code P0128 to come up,unless you have an intermittent problem.A reading of the freeze frame data ,when trouble code caused the light to come on would be one of the things to find out. It would show the coolant temperature when the light came on.The idea of testing is to compare the coolant sensor reading with the actual coolant temperature. I will send you the testing procedure from the service information,you will see what it involves.I would ask the dealer to diagnose and tell you what they find for the reason the code is being set.