Fremont Motors explains in a recent blog post just what, exactly, TPMS means.
TPMS stands for Tire Pressure Monitoring System, which is found on all consumer vehicles sold in the past 10 years. As the name implies, TPMS keeps track of tire pressure and alerts the vehicle when one or more tires have low pressure. When tire pressure is 25 percent less than recommended for the vehicle, a yellow alert light appears on the vehicle's dashboard.
Two different TPMS exist direct and indirect. For the direct method, a sensor on each wheel sends a radio frequency to a receiver in the vehicle. The indirect method uses other sensors already in place to detect differences in the rotation speed or diameter of one of the tires. This method may be less accurate if all four tires are equally low on air.
Some vehicles display the tire pressure for each tire in a dashboard diagram. Other versions just show a warning light without indicating which tire has the issue.
TPMS systems come in handy as they can alert the driver to potential issues such as punctures or slow leaks. Once a wheel is replaced with a spare, the TPMS will not function properly.