Washer fluid sensor says low when full....

[Jzza4]

But does nothing when empty.

What gives?

[shogun]

Probably the float is full of water and does not float. Use a flashlight and see if it floats or hangs.
Also remove the plug from the sensor and bridge it with a short cable. Then the alarm should disappear. If not, probably the thin wires are broken.
Check also if the float is correct installed towards the bottom.

[DaveVoorhis]

The sensor is in upside down. Pull it out, see how it works, put it back the right way.