| May be a silly question but had you ever checked the tyre that was underinflated (as you say the car was new)? It may have been delivered underinflated and the cold snap took a few pounds of pressure out which triggered the alarm. Alternatively there could have been a small amount of dirt in the valve which allowed a slow deflation. You could try putting some air in and then releasing some of it to blow out any dirt and then re-inflate to correct pressure so that you were sure the valve was seating properly. If it is still a problem and there is no obvious damage I would take it back and ask for a new tyre. | 
