One other thing to try is simple.

Key in and turn to Pos 2, put your seatbelt on and by that time all the systems should have completed their boot-up and tests, then start the car. Sometimes if you catch the systems at the wrong moment they can throw spurious errors.

I do this all the time now and very, very rarely get a warning about Oil, or Air Suspension - another favourite.

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Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
Current: 2012 R80 Countryman SDX Green/Cream