My coolant light has been coming on and off sporadically.

I've had it pressure tested twice at two different locations weeks apart and no leaks were found. I've replaced both the thermostat and the ETC, but the light still comes on. The old ETC was broken when I replaced it. The coolant level is normal, engine temp is normal, no signs of leakage. Prior to replacing the thermostat, the engine temp rose momentarily to 120 degrees, the cooling fans at the front of the engine went into overdrive, and the A/C system would only blow cold air, no matter at what temp the climate controls were set. Problems went away with the new thermostat and I replaced coolant lost during both the ETC and thermostat replacements, but the coolant light is still on. Coolant level and engine temp are still normal.