Yes, the sensor I was referring to - that I replaced - is the level sensor in the expansion tank (#3 in diagram). I assumed that was the one creating the message about the "level" of coolant. Is there another sensor somewhere that might generate the same message wording? Is there a "level" sensor in the radiator itself or elsewhere? Is this an error code that must be cleared manually? Thanks again.

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2006 X5 4.8is
LeMans Blue over black
Style 168 rims
Blackout grills and hood vents
Aux jack