GTC Coolant temp sensor

[chris_yorks]

Hi,
Daughter's 2012 GTC had what I thought to be a faulty coolant temperature sensor. Error shown on display and fan running at full speed constantly. Purchased a new thermostat with sensor included and connected it to the cables (before going to the trouble of fitting thermostat to engine block) to test.
The same error was still shown on the display, and the fan ran at full speed.

Sensor resistance very similar to the fitted one. (17 ohms) at room temperature.
Appear to be getting voltage at the cable plug.
All seems as it should be.

Is there a way of resetting the error.

Thanks


 A little more info...The error code is P0128. With "A/C off due to high temp" displayed and rad fan running at full speed.
Temp gauge on dash shows 50 degrees and doesnt move.
Have since changed thermostat (the old was in fact open slightly when removed and cooled down).
Symptoms the same.
I believe there is another sensor at the radiator - should I change this one?

Any info would be greatly appreciated. 
Thank you.