You topped off the air in your tires, but a few days later, you notice that one of them is low again. It could be a hole, but before you go through the hassle of searching for one or making an appointment at the tire shop, first check for a leaky valve stem. ร‚โ‚ฌล“รขโ‚ฌยฆ to determine if the valve stem is the cause of your deflating woes, remove the cap.