Yep, circuit high means that the voltage on the wire is higher then expected. Broken wire or bad sensor will cause this. Sensor changes resistance based on temperature. Low temperature is higher resistance. Broken wire will max out the resistance and thus make it read the lowest temp it can. If it stays there too long or there is a mismatch between the air intake temp sensor the ecm can tell something is wrong.
The coolant temp sensor is right behind the oil fill cap. Take the plug off and measure the voltage at the plug and the resistance at the sensor. One wire should have either 5 or 12 volts, dont remember, and the other should be a return to the ecm i believe. That last wire is likely broken if you have good voltage on the other and the sensor seems good if you have no voltage on any wire then the one that supplies the power is broken
It could also be as simple as it being unplugged or another connector like the large bale connectors on the top driver side of the engine has a bad connection/pin
