All I gotta say is...LUCAS.
The other thing to watch is the sensor colour...early one where white and then they went to black.....they do NOT interfit.....although MB will tell you they do.
The different resistence between the 'coolant' and 'washer' make the correct light come on.Trouble is, as has been explained...the failing sensor will change resistence fooling the monitor. From the few I have repaired, it seems the default is COOLANT LOW.
FWIW and FYI....Mice seem to like to chew the wiring under the plastic covers...and there's a ground post there too.....lift off the cover and check....they seem to like living in the HAVC system plenum.
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