My coolant temp needle, when its not accurate, will just sit below C. When it feels like it wants to work, it will work, but most of the time it will read really low (around 1/8th from C to H), it mostly does this after getting onto the freeway, but only when the reading is accurate. Could this be my gauge, sending unit, or sensor? Coolant is topped off

 

Does the heater work when the gauge is showing cold? --- If the heater is not working after a reasonably period of time, then the thermostat is probably stuck open.

If the heater works after the engine warms up and the gauge is showing cold, then go check out the sensor and/or its connector first. If you remove the wire the gauge should go to either full hot or full cold. If you ground the wire the gauge should go the opposite. If all this checks out, it is probably the sending unit/sensor. If you can't get movement on the gauge with either an "open" or "closed" sensor wire, then the wiring to the gauge is suspect or the gauge itself is bad.

My experience has been that the thermostat is probably open, or the sending unit needs to be replaced if all the other gauges are working. I hope this helps and good luck.

 

This is very helpful information!

The car drives as normal; the heat and ac work beautifully. My only question is which is the temp sensor I need to check?

 

To my knowledge, the temp sensor for the gauge is the one that the red arrow points to:


Here is the link from the thread that I got this photo:
https://honda-tech.com/forums/honda-...nsors-3383233/