Merc cl500 coolant level warning wrong

I have a Merc CL500 with the Coolant level warning displayed on the dash, although the level is correct. A new sensor has been fitted, but the problem still remains. There seems to be no fault with the wiring around the sensor. There is 12v at the plug, but this drops to 1.7volts once it is plugged in. Has anyone had a problem like this?

Managed to trace this problem to the cooling fan!!! Even through the vehicle never showed any signs of over heating and the symbol looked like low fluid, I found that the cooling fan was siezed. Ordered new fan from Merc dealer and are now waiting to fit it. Sometime miss direction can send you looking at the wrong things and over looking the real fault. Oh well thats life!