P0118 coolant temp code on 2000 Mazda 626

Hi everyone! Can you tell me what this code means, where the sensor is located, and how it affects the running of the engine? I would appreciate any feedback I get.

Asked by for the 2000 Mazda 626
in most cases, this code is from a thermostat stuck open. the engine never heats up to the proper operating temp. i would check the temp when hot before replacing anything.

Thank you Roy...we will check the temp as you suggested. I appreciate your feedback!