Introduction to TPMS

A tire pressure monitoring system (TPMS) is an electronic system designed to monitor the air pressure inside the pneumatic tires on various types of vehicles. It warns the driver of significant loss in tire pressure in one or more tires which can lead to dangerous road situations and accidents if not corrected promptly. Modern TPMS sensors mounted on each wheel send continuous radio frequency signals to a central receiver in the vehicle. The receiver processes the signals and alerts the driver if pressure falls significantly in any tire through illuminated symbols on the instrument panel or dashboard.

How does a TPMS work?

Each tire is fitted with a battery-powered TPMS sensor which contains a pressure sensor, microprocessor, and radio frequency transmitter. The sensor measures the Automotive Tire Pressure Monitoring System  in its respective tire and transmits this as a radio signal to the vehicle's receiver unit using an identification code unique to each sensor. The receiver determines the tire pressure readings from these signals and compares them against pre-set thresholds stored in its memory. If a tire drops below the pressure threshold, usually around 25% underinflation, the receiver alerts the driver by illuminating a low tire pressure warning symbol.

Direct vs Indirect TPMS

There are two main categories of TPMS in use - direct and indirect systems. A direct TPMS has sensors mounted inside each tire that measure pressure directly. This provides the most accurate pressure readings as the sensors transmit data continuously while driving. However, direct systems require wheel removal for sensor battery replacement every 5-7 years which increases maintenance costs. Indirect or "smart" TPMS do not have in-tire sensors. Instead, they monitor tire pressure indirectly based on wheel speed sensors and ABS sensors in the vehicle which provides data on each wheel's rolling radius. This data is analyzed by a central computer to detect pressure drops in underinflated tires. Indirect systems are cheaper but provide less precise pressure readings compared to direct systems.

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