2008 ford fusion thermostat

the check engine light is on. i had autozone put their code scanner on it and it read p0128, which is “low temperature”. and the temp gauge is moving around a lot, not significantly hotter than nomal, but sometimes rapidly moving towards cooler, then creeping back to normal again. i feel the error code is probably accurate, and not a faulty sensor because of what the temp gauge is telling me. where it appears the top radiator hose enters the engine is tucked tightly under the power steering pump in a very difficult to access area. i was hoping there is some other clever and easy to get to location for the thermostat where i hadn’t thought to look.