Every year during winter, one of the TPMS stem valves on tires fails from the inside and starts leaking air. I have had to replace one each and every year for the last three years. I believe it is either the structure or the material of the TPMS sensor that causes the problem. The first year I was covered by the warranty but last two times I had to pay for labor and material for around $40 at local dealer to fix. One time this happened during a road trip, and another happened just before a road trip when checking pressure at a gas station.