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Click the stalk button until you get to the Check-Info option then long-press. Cycle through to the Check option and long-press. That will bring the warning up on the tach screen.
Could be that it is below 37F. I know that at that temp, the car "bongs" at me and shows that little symbol in the tach. IIRC last winter it stayed there but I didn't always get the "bong" when I started the car.