2001 Mercedes Benz CLK320 Radiator Water Sensor Level locat

The "Check Coolant Level" indicator comes on, so I check the coolant level and it fine.

Throughout my scouring the Internet for information it appears to be the sensor. The parts book says.2 of time to replace which isn't much time.

I've check under the hood and I can't find the location the 'plugin' sensor. I would assume (I know bad word) it would be near the overflow/fill-up container.

Can use your help on where the location is