Change thermostat & clutch trailblazer engine light still came back on showing P0128

Question

What other possible problems?

Answer 1

i have seen several coolant temperature sensors faulty on these engines. this code pertains to the heating up of the coolant system in an adequate amount of time. as long as the radiator has flow and the water pump is pumping the coolant should heat up correctly in the allotted time. make sure full of coolant and check temperatures of hoses after thermostat opens. if temperatures are correct the coolant temperature sensor is probably at fault. Did you use a quality thermostat?