ford fusion code PO128 how do I check the circuits thermastat is new

Question

I have replaced the thermostat. fluid level good. how do I check the circuits or what do I do next.

Answer 1

P0128 Coolant thermostat below thermostat regulating temperature

If you have a scan tool that reads datat read the coolant temperature. Here is a Fusion FWD 3.0 Here is  a connection of the coolant temperature sensor  that was not making good contact , The reading was showing it is -40 degrees F. Replacing the ECT solved the problem. and cleaning the connection so it can make proper contact.