Tire presure sensor on 2008 Subaru Forester

Ever since it started getting cold here in the Northeast (mid December ish) my tire pressure sensor light is on. I know that it may be necessary to add air during cold weather as the air in the tire can contract in the cold but the pressure is fine - I had my mechanic check it out. Light does go out when it warms up - at least above freezing - but comes back on again when it gets cold. Normally I spend most of the winter in Florida but am usually here (in MA) until mid Jan. and this has never happened in previous years. Thank you. Gail

@geo999

This is a classic scenario. Driver fills up tires in the afternoon, after driving for awhile, and the tires are hot.

In the morning, when it’s cold, the tire pressure is lower. And that’s when the light comes on

Fill up all the tires when it’s cold . . . BEFORE the car is driven

If you have sensors in the tires, include your spare too. Still no guarantee. They are a PITA.