Does your scan tool give you the engine temp values to see what it is seeing? Before you begin the long journey to the temp sensor did you replace the thermostat with a new one? I have to ask, as simply getting to the coolant temp sensor will be the biggest challenge as it is underneath the intake manifold. You will need to get at it from under the car and measure the resistance at the sensor. The thermostat however is a five minute swap and should fix it.