Which means the first step is to sniff for coolant smells on the outside and fix that first. If you can smell it outside, it will get inside. Even in recirculate mode, it won't cut off all outside air.Another source of odor in the winter is the coolant tank cap. O-rings are notoriously bad at sealing when temperatures drop - just ask NASA. My 2012 ECO MT doesn't loose any coolant during the summer but it definitely seeps around the o-ring in the tank cap in the winter. The main cabin air intake is about a foot directly behind this cap.