To ensure that your vehicle's TPMS system's pressure sensors remain operational for as long as possible, always reaffix the valve-stem cap after checking air pressure or inflating the tires. This indicates that the suspect tire's circumference has changed and that it could have lost air pressure. It does not employ tire-pressure sensors in the tires, relying instead on the anti-lock-braking system's wheel-speed sensors to determine if any particular tire's rotational speed is out of sync with the others. There is a second type of tire-pressure monitoring system, which works entirely differently.
Inflation pressure recommendations for the tires that originally come on a car can usually be found on a label on the driver's doorsill. In the event that the sensor detects that air pressure in a tire has dropped to a dangerously low level-25 percent below the recommended air pressure, according to federal government regulations-a warning message or light will display in the instrument cluster. Tire-pressure sensors are usually attached to the valve-stem assembly of each tire and are powered by batteries. Millions of these systems have been fitted to passenger vehicles since the 2008 model year, when they were made mandatory in the United States. Tire-pressure sensors are integral to what is known as the Tire Pressure Monitoring System (TPMS). It reads out in pounds per square inch (psi), and it illuminates an amber warning light to alert you if one or more tires are low on air. The sensor transmits that information via low-frequency radio to the vehicle's onboard computer and, if the car has one, to a corresponding display in the instrument cluster. A tire-pressure sensor is a small programmable electronic device, located in the pressurized pocket made by a wheel and tire, that constantly measures the air pressure inside the tire.