Hi, Mary. It sounds like either there is a bad connection at the sensor or the sensor itself is bad. I do have a concern that the coolant was low again. Is there any evidence of a leak? Have you ever noticed white smoke from the exhaust? If you check the motor oil, is there anything that appears to be creamy or tan in color?
As far as the sensor, it is easy to replace. Above, I provided a location pic for you. You will lose coolant when it's removed so you have two choices. First, when the old one comes out, have the new one ready to put in as quick as you can to limit the amount of coolant lost. Or, you can drain the radiator to a level below the sensor level.
I attached a pic of what the sensor will look like. Just disconnect the electrical connector and then unscrew it from the engine and reverse the process for install. I circled the point on the sensor where you will place the wrench. I can't remember the exact size wrench you will need, but it will be near a 1" open end wrench. I don't think a deep well socket will fit over the connector area.
However, since it didn't read at all today, before replacing it, just make sure the wiring/connector isn't damaged.
I hope this helps. Feel free to let me know if you have other questions and also if there is evidence or a leak, anything odd about the oil in the engine, or if you notice white smoke from the exhaust.
Let me know.
Joe
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Sunday, May 24th, 2020 AT 8:43 PM