How is the TPMS sensor working?
The primary function of TPMS sensors is to alert you when a tire is underinflated, reducing the risk of blowouts and improving fuel efficiency. There are two main approaches: direct TPMS sensors that physically measure air pressure inside each tire, and indirect TPMS systems that infer pressure status from wheel-speed data collected by the vehicle’s ABS/ESP system.
Direct TPMS sensors are mounted in or on the valve stem and continuously monitor the tire’s pressure (and often temperature), sending wireless signals to the vehicle’s TPMS control module. Indirect TPMS relies on analyzing differences in tire rolling behavior to flag potential underinflation, without a dedicated sensor inside the tire. Both approaches aim to provide timely warnings, but they differ in precision, maintenance needs, and how they handle tire changes or sensor replacement.
Direct TPMS: In-tire sensors that measure pressure
Direct TPMS delivers tire-specific pressure readings by placing a sensor inside each tire. These sensors capture actual pressure (and sometimes temperature) and wirelessly transmit the data to the vehicle’s computer. The system needs a power source and is designed to survive the demands of driving, temperature swings, and tire changes.
Core components and how they function together are listed below:
- MEMS pressure sensor that detects air pressure inside the tire
- Temperature sensor to compensate readings and monitor tire heat
- Microcontroller that processes measurements and formats data for transmission
- RF transmitter and antenna to send data to the vehicle over a low-power link
- Valve stem assembly and mounting hardware for secure in-tire placement
- Battery, typically a long-life lithium cell, powering the unit for several years
Direct TPMS sensors provide precise, tire-by-tire readings and enable rapid, location-specific warnings. Their biggest constraints are battery life and the eventual need to service or replace sensors when tires are changed or batteries degrade.
Indirect TPMS: Estimating pressure from wheel-speed data
Indirect TPMS uses the vehicle’s ABS/ESP wheel-speed sensors to infer tire pressure status. Rather than measuring pressure directly, it looks for changes in rolling radius and traction characteristics across tires. When a tire’s pressure drops enough to alter its effective circumference, the system can flag a potential underinflation even without a physical sensor in the tire.
The indirect approach relies on several data streams and analytical steps, summarized here:
- ABS/ESP wheel-speed and steering data to assess each tire’s rotation
- Algorithms that compare the rolling radii of all tires under various driving conditions
- Estimation of pressure loss and triggering of the low-pressure warning when anomalies exceed thresholds
- Calibration or relearn requirements after tire changes or unusual wear patterns
Indirect TPMS is generally cheaper to maintain because there are no sensors inside the tires, but it cannot provide exact pressure readings. Its accuracy depends on tire wear, load, and driving conditions, and it may be slower to warn in some scenarios.
Data flow, relearn procedures, and modern trends
In most newer vehicles, a direct TPMS sensor communicates with the vehicle’s TPMS control module via a low-power radio frequency (commonly in the 315 MHz band in North America or 433 MHz in many other regions). Each sensor has a unique identifier that the car learns and associates with a specific wheel position. When tire service is performed—rotation, replacement, or sensor maintenance—the vehicle may require a relearn or sensor programming step so it correctly maps sensor IDs to wheel positions. Some brands also support smartphone apps, NFC tools, or scan tools to assist with sensor identification and relearn procedures.
Going forward, the industry is pursuing longer-lived, more robust direct sensors and more seamless relearn workflows. Some newer implementations explore energy-harvesting or batteryless concepts, but the vast majority of current systems still rely on batteries with 5–10 years of expected life. Indirect TPMS remains a cost-effective option, especially on older or budget vehicles, though it won’t replace the detailed data that direct sensors provide on a per-tire basis.
Summary
TPMS sensors protect you from underinflated tires by warning promptly and helping drivers maintain proper tire pressure. Direct TPMS offers tire-specific pressure readings from sensors inside each tire, plus occasional temperature data, while indirect TPMS deduces pressure status from wheel-speed data without in-tire hardware. Both systems require calibration and can necessitate relearn steps after tire service. Together they represent a key safety feature that supports better fuel efficiency, tire longevity, and overall vehicle handling.
