How does TPMS actually work?

TPMS monitors tire pressure and alerts you if it drops below a safe level. There are two main approaches: direct sensors in each tire and indirect methods that infer pressure from wheel speed.

Direct TPMS vs Indirect TPMS

Two main approaches exist to monitor tire pressure. The following sections summarize how each works, what data they rely on, and how they communicate with the vehicle's computer.

• Direct TPMS (D-TPMS): Each tire has a pressure sensor mounted in the valve stem or inside the wheel. The sensor measures the tire pressure (and often temperature) and transmits a radio signal to the car’s TPMS control module. The system can display per-tire pressures in compatible dashboards and triggers a warning when a tire drops below a factory-set threshold, typically relative to the vehicle’s recommended cold pressure. The sensors are battery-powered and used for several years, but batteries can fail and sensors may need replacement after tire service or wheel changes.


• Indirect TPMS (I-TPMS): No in-tire pressure sensors are used. Instead, the system uses the ABS/ESC wheel-speed sensors to detect changes in each tire’s rolling circumference that occur when a tire is under-inflated. The system learns a baseline when tires are properly inflated and then flags a warning when it detects a deviation. Indirect TPMS does not provide actual psi readings and can be affected by tire wear, temperature, or mismatched tires; recalibration is often required after tire rotation or replacement.

In practice, direct TPMS provides exact tire pressures, while indirect TPMS offers a lighter-weight solution without in-tire sensors, trading exact readings for broader coverage and lower maintenance needs.

How a TPMS warning is triggered

When the system suspects under-inflation, it follows a sequence to alert the driver. The exact steps can vary by vehicle, but the general process is similar across manufacturers.

• The tire’s pressure (direct sensors) or wheel-speed pattern (indirect) deviates sufficiently from nominal values.


• The TPMS control module interprets the data and determines whether a warning should be issued.


• A warning light or message appears on the dashboard, and in some cars the system may also display per-tire pressures (direct TPMS).


• The driver is expected to inflate tires to the recommended cold pressure and recheck; many systems automatically reset after inflation once the vehicle detects appropriate pressures or completion of a relearn procedure.

Warnings are intended to prompt corrective action before a tire under-inflation causes poor handling, increased wear, or a blowout risk. If the warning persists after inflation, there may be a sensor fault or a system calibration issue that requires service.

Maintenance and best practices

Keeping TPMS accurate requires routine tire maintenance and an understanding of how your system works. Here are practical guidelines to keep the system effective.

• Regularly check tire pressures with a gauge, especially before long trips or when temperatures change significantly.


• Direct TPMS users should note that sensors have finite battery lives and may require replacement after several years or if a tire is replaced or a bead seal is broken.


• Indirect TPMS relies on calibration; after rotating tires, replacing tires, or changing tire sizes, a relearn or calibration procedure is often required, which may be automatic or performed via a menu in the vehicle’s settings.


• Understand the acceptable range: the threshold to trigger a warning is typically around 20-25% below the vehicle’s recommended cold inflation pressure, but exact values vary by model; always refer to the owner’s manual or the door placard for your car.


• If a TPMS warning occurs with properly inflated tires, have the system checked by a professional to diagnose a faulty sensor, a damaged wiring harness, or a dead battery in a direct sensor.

Proper tire maintenance protects the TPMS' effectiveness and helps ensure tire longevity and vehicle safety.

Summary

TPMS keeps drivers informed about tire pressure using either direct sensors that report actual psi or indirect methods that infer pressure from wheel dynamics. Direct TPMS provides precise readings and can warn per tire, while indirect TPMS relies on calibration and may not show exact pressures. Regular tire inflation checks and appropriate system maintenance — including sensor battery life, calibration after tire changes, and attention to warning lights — help maintain tire safety and efficiency.

How does TPMS work without sensors?

Indirect TPMS (iTPMS) systems do not use physical pressure sensors; they measure air pressures using software-based systems, which by evaluating and combining existing sensor signals such as wheel speeds, accelerometers, and driveline data to estimate and monitor the tire pressure without physical pressure sensors in ...

How do TPMS sensors know which wheel they are on?

Each sensor has a unique serial number. This is how the system not only distinguishes between itself and systems on other vehicles, but also among pressure readings for each individual tire.

How does the TPMS sensor work?

TPMS sensors work in two main ways: direct and indirect systems. Direct systems use a sensor inside each tire to measure pressure and transmit the data wirelessly to the car's computer. Indirect systems use the vehicle's existing wheel speed sensors to monitor tire rotation; a low-pressure tire rotates faster, and the system detects this difference to trigger a warning. 
This video explains the basics of TPMS and how direct and indirect systems work: 47sCars SimplifiedYouTube · Apr 9, 2022
Direct TPMS

• How it works: A dedicated sensor is attached to each wheel and directly measures the air pressure inside the tire. 
• Data transmission: The sensor uses a battery-powered transmitter to send the pressure and temperature data wirelessly to the car's receiver. 
• Advantages: This system is more accurate and can show the real-time pressure and temperature for each specific tire on the dashboard. 
• Disadvantages: Sensors can be more expensive to replace, and their batteries have a limited lifespan (5-12 years). 

This video shows what a direct TPMS sensor looks like inside the wheel: 1mCars SimplifiedYouTube · Aug 4, 2018
Indirect TPMS

• How it works: This system leverages the vehicle's anti-lock brake (ABS) wheel speed sensors, which already monitor how fast each wheel is rotating. 
• Data analysis: The computer compares the speed of each wheel. A tire with low pressure will have a smaller diameter and will therefore spin faster than the others. 
• Advantages: It is a less expensive system to manufacture and doesn't require its own sensors in the wheels, so there are no batteries to replace. 
• Disadvantages: It is not as accurate and typically only indicates that there is a low-pressure problem, without providing specific readings for each tire. It also requires a reset after a tire rotation or inflation to recalibrate. 

This video explains how indirect TPMS works by comparing wheel speeds: 58sLurgs How To GuidesYouTube · Oct 26, 2018

Why is my TPMS light on but tires are fine?

Your TPMS light may be on despite your tires being properly inflated due to a malfunctioning sensor, a dead sensor battery, a recent tire rotation, or extreme weather conditions. A sensor can become damaged from impacts or age, a dead battery can prevent it from sending a signal, and in cold weather, air contracts, which can trigger the warning. A recent tire rotation might also cause a temporary alert that requires a reset. 
This video explains some common reasons why your TPMS light might be on even if your tires appear to be fine: 58sFixITYouTube · Jan 18, 2025
Common reasons for the TPMS light to stay on

• Sensor Malfunction: The sensor itself can be faulty due to age, damage from impacts, or corrosion, causing it to send false readings. 
• Dead Sensor Battery: Each TPMS sensor has a small battery that typically lasts 5 to 10 years before it needs replacement. 
• Weather Changes: Cold temperatures cause air to contract, leading to a drop in tire pressure that can trigger the light even if the tires appear fine. 
• Recent Tire Rotation or Replacement: If the tires were recently rotated or replaced, the system may need a few miles of driving or a manual reset to recognize the new tire positions. 
• Valve Stem Issues: A slow leak from the valve stem can cause the pressure to drop gradually, keeping the light on. 
• Improperly Inflated Spare: If you recently used your spare tire and didn't inflate it, the system may trigger the light. 

You can watch this video to learn how to check your TPMS settings and perform a manual reset: 52sHondaYouTube · May 15, 2019
What to do

1. Check all tires and the spare: Use a tire pressure gauge to check the pressure in all four tires and the spare. Inflate them to the recommended pressure listed on the sticker inside your driver's side door jamb. 
2. Drive for a few minutes: After inflating the tires, drive the vehicle for 10-20 miles to give the system time to recalibrate. Some systems will reset automatically, while others may require a manual reset. 
3. Perform a manual reset: Some vehicles have a "TPMS Reset" button, often located in the glove box or on the dashboard. Pressing and holding this button for a few seconds may resolve the issue. 
4. Seek professional help: If the light remains on, take your vehicle to a professional to diagnose the problem. A mechanic can pinpoint a faulty sensor or a slow leak that is not immediately visible.