At this price we replaced all four for the price of "each" at the dealer. It's worth doing all four at the same time as the battery inside will likely die soon on all the other tires as well. In our 2010 Toyota Matrix, after resetting the TPS, the onboard computer took about 30 minutes of driving to recognize and learn the sensors. So don't be alarmed if they don't work right away. Now I can head into New England winter with confidence.