My 94, 740I's Coolant level indicator is on all the time saying "Check Coolant Level", the coolant level is fine and the running temperature is normal. I have taken the sensor tube out of the top of the Coolant reservoir, checked the slide that follows the collant level, it moves freely - everything seems in order. I unplugged the wires to the sensor and shorted them, the warning went off. So, the problem seems to be with the sensor.
How does the slide on the level sensor tube send the level information?
There are no wires attached or switches that it makes contact with. It's just a free moving, non metallic collar. Is there a way to further test it?

You coolant sensor is bad.

I've replaced about a thousand of them over the years.

i had the same problem .my mechanic charged me @ $81.00 to replace it,