P0118 Code Engine Coolant Temperature Circuit Fault

I replaced my coolant after winterizing my 2009 2.7L truck and the next day I had a check engine light and P0118 code, which is P0118 Engine Coolant Temperature Circuit High Input.
Probable Cause:
1. Open Circuit Condition
2. Faulty ECT Sensor
3. Faulty ECM

I only used the radiator drain plug to drain the coolant. I got 5 quarts out and added 5 quarts of Toyota Super Long Life Coolant back in. After reading the FSM, it looks like I didn't really add coolant correctly (I just slowly adding, I didn't squeeze the radiator hoses or anything).

Looking at the FSM, I can check the Engine coolant Temperature sensor, but since I didn't use Engine Drain plug, I don't think I would have bumped this sensor or anything.
http://www.customtacos.com/tech.old...6toyrm/06toypdf/06rmsrc/rm2006ta/00500510.pdf

The FSM is rather vague on the other causes. I don't know what the circuit on the coolant system consists of.


Any advice on trouble shooting or further diagnostic?

Thanks.