2013 XF 3.0T AWD, coolant level sensor

The issue started couple months ago - just a nice, dire red triangle on the dashboard, “coolant level low”. Sometimes it would go away, then it would go back, now it is here to stay (last couple of weeks). There is absolutely nothing wrong with coolant level or coolant quality (5000miles of normal driving, couple ~400mile trips). looks like a faulty sensor - where is this thing located and what is the replacement part?

Turns out it wasn’t the sensor but the float inside the reservoir. Took a thick copper wire and a little bit of wiggle to unstuck it. Seems to be working fine.