I too had this code. Started with the Engine Hot / AC Off. Then a few weeks later the engine like came on also. I connected my code reader and it displayed the PO0128 twice. During this period i noticed that my thermostat gauge wasn't responding either. I cleared the code and the thermostat is now responding normally and neither message has come back. Is this a common occurrence?

 

most p0128 problems are thermostat related but it can be electrical. If I were to hazard a guess without diagnosis; replace the thermostat