I believe if your coolant sensor is the round type (one with 4 pins) you need to check the resistance across each or the two opposite pins (for example if you draw a diamond shape with each pin represents each corner, then you'd want to test the two opposite pins and not the adjacent ones). The resistance should vary depending on the engine (coolant) temperature. So you first check when engine is cold, then check when you start the engine and coolant starts warming up etc.. each time write down your measurements (for both sets of pins). If you see the resistance values don’t change, then the sensor is bad. from what you described above, you either have a bad sensor or bad wiring/connector that plugs to the sensor. I'd change the sensor anyway since it's only about $15 or so. Good Luck and let us know what you come up with.

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Joe95E420