I continue to receive an engine code - P0128 with the check engine light. on 2004 Suzuki Verona

I have replaced the radiator (new), replaced the Antifreeze with the green 50/50 mix and the radiator/thermostat temperature sensor. I am told that the fluid in the radiator is not warming up fast enough? How do I get the light to stay off? thanks

Asked by for the 2004 Suzuki Verona
poss thermostat is stuck open and not leting coolant get hot right away