Code 128
 

Hello there felllas, recently i got code 128, i attempted to clear it with my scangage but there is no response. I am guessing, the thermostat is staying the open position; however, temp in my truck on a normal drive is flactuating from 160 to 180, sometimes hit 190. any ideas as it could be caused by something else?

i know the code has to do with coolant temp.

thanks,