How long has the warning been illuminated? Is this just something that started happening very recently? Do you have different winter rims, or are these the original rims that came with the car? If winter rims, do you have extra sensors in them, where are your OEM rims stored in relation to where you park your car (proximity). This could be TPMS sensor issue depending on what answers you give.
2012 Focus SEL 5 door 303a w/Lux pkg in KonaBlue
2012 Escape Limited w/park assist
2010 F150 Supercrew XTR 5.4 4x4
2008 Kawasaki Concours 14 (street)
2008 Kawasaki ZX10R (track only)