The EXACT SAME THING happened to my wife's Matrix. when I took the flat tire to Discount Tire, they told me the problems with these things. They were nice enough to pump up the flat tire, remount it, and put new stem caps on.....all for freeSgt_Beavis said:On paper they work fine. In the real world, they can be a problem. My wife and I took her Matrix in to have the oil changed at a Kwik Lube. They did the whole service including checking the tire pressure. About 10 miles after we left, we discovered that one of our tires was flat. The guys at Discount Tire told us that the caps are fine IF you screw them on perfectly. They said it was easy to get a bad seal on the tire valve and get a slow leak. I've got 4 of them in my glove box now. You can have them for free if you like.
Oh, they are made of plastic, so if some road debris hits them, I don't think they are gonna stand up to it. In other words, make sure your spare tire is good.