TPMS Tire Pressure Monitoring System
The Tread Act requires that vehicles built after 2007 include a direct TPMS Tire Pressure Monitoring System that has tire pressure monitoring sensors placed inside each wheel assembly. It monitors a vehicle's tire air pressures and illuminates an amber TPMS light or audible chime to inform the driver if a tire's underinflated (or overinflated).
The system includes a receiver located inside the BCM or keyless entry system and an amber warning lamp. The sensors send an RF signal to the receiver including information like sensor ID's and air pressures at regular intervals.
They include a lithium-ion battery that can last up to ten years. As these batteries wear, they're less able to communicate with the receiver. The control module will illuminate the TPMS light if communication is lost. If the light stays on continuously, inflate all tires to the specifications found on the door sticker, including the spare. These are the required values the direct system uses for that models tire pressures.
TPMS sensors have a port to sense the tires air pressure. If it becomes clogged, the sensor will indicate low air pressure to the module, and the TPMS light will illuminate. Check a suspect tire for debris or an older flat repair product that can clog the sensing hole in the sensor.
Some older models use an indirect system that utilizes the vehicle's wheel speed sensors to estimate air pressures. This system is based on the principle that a tire with low air pressure spins faster than one that's filled.