I think that the two experiences are unrelated - here's how:

If you check the oil right after shutdown it will read relatively low because it takes a long time for all of the oil to drain back down into the pan. How long depends on many factors but some say that with synthetics it can take overnight before all of the oil drains back down. I would say if you waited at least 10-15 minutes after shutdown to read the dipstick that you will probably have gotten a fairly accurate read, though it might still be lower than it would be if it sat overnight. So, is it possible that your first reading was made right after you shut the engine down and the second one after an extended period where the oil drained back down??? If so, that would explain the different readings.

As for the low-oil level warning - I believe the oil level would have to be well below the "add" mark before that warning should be triggered. I've removed the sensor that triggers the low oil warning and it is a float on an arm attached to a switch. Based upon my observations the oil would have to be 2-3 quarts under "full" before the low oil warning would be triggered, or at least 1-2 quarts under "add" on the dipstick. You might have a faulty connection at the sensor or a bad sensor causing a false alarm. That would be my guess anyway. I would say if it goes on again have the sensor checked and replaced...it does not take very much time to replace it (30 minutes max including lifting the car) so it would probably cost about $50 plus the cost of the part to replace it.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz