check oil level message comes on but oil level is max on 2007 Mercedes-Benz E350

I drove from Boston to NY this weekend but the check oil level message came on but the oil level is to the max when I checked.

I suspect that the system uses a float in the oil pan to determine the oil level and it's sunk. The other possibility is that the warning system has an electrical failure in the module but a sunken float is more likely.
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1 more answer
oil level sensor may be bad, there is no float.