How Tire Pressure Sensors Work: The Technology Keeping Tires Safe and Efficient

Tire pressure sensors monitor the air pressure (and often temperature) inside each tire and send that data to a vehicle’s control unit via radio signals; if a tire is underinflated, the system triggers a dashboard warning. Most vehicles use either direct sensors mounted at the wheel that measure pressure with a tiny MEMS transducer, or indirect systems that infer pressure from wheel-speed data. Here’s how the hardware, software, and regulation fit together.

What a Tire Pressure Sensor Does

A tire pressure monitoring system (TPMS) is designed to alert drivers before underinflation compromises safety, fuel economy, or tire life. Underinflated tires run hotter, wear faster, and lengthen stopping distances. TPMS automates checks that most drivers don’t perform regularly, providing real-time or near-real-time status for each wheel.

Two Approaches: Direct vs. Indirect TPMS

Automakers deploy two main types of TPMS. While they share the same goal—detecting underinflation—they work very differently and have distinct strengths and trade-offs.

• Direct TPMS: Each wheel has a battery-powered sensor that directly measures air pressure (and typically temperature) and transmits readings to the vehicle via radio frequency (RF), historically at 315 or 433 MHz, and increasingly via Bluetooth Low Energy (BLE) on some newer models. It offers per-wheel accuracy and fast leak detection.
• Indirect TPMS: No in-tire sensor is used. Instead, the car analyzes ABS wheel-speed signals and other dynamics to infer a change in rolling radius caused by low pressure. It’s lighter and cheaper but needs driver calibration after pressure changes and can be less precise.

Direct systems are more accurate across conditions and provide exact pressures, while indirect systems infer pressure changes and are more sensitive to uneven tire wear or loads if not properly calibrated.

Inside a Direct TPMS Sensor

Direct sensors pack multiple components into a compact, robust module attached to the wheel (valve-stem or band-mounted). Each part enables accurate, battery-efficient monitoring in a harsh environment.

• MEMS pressure transducer: A piezoresistive or capacitive micro-machined diaphragm converts internal tire pressure into an electrical signal.
• Temperature sensor: An onboard thermistor improves accuracy through temperature compensation and enables temperature warnings on some vehicles.
• Accelerometer: Detects wheel motion to wake the sensor, adjust transmit intervals, and help identify which wheel position the sensor occupies.
• Microcontroller/ASIC: Digitizes signals, applies calibration and compensation, packages data with a unique ID, and manages power.
• RF transmitter and antenna: Sends data bursts to the car’s receiver. Legacy systems use ASK/FSK modulation at 315/433 MHz; some newer designs use BLE at 2.4 GHz for faster pairing and over-the-air features.
• Low-frequency (LF) receiver (often ~125 kHz): Allows the vehicle or a service tool to wake or address a specific sensor during pairing/relearn.
• Primary cell battery: Typically lasts 5–10 years depending on drive cycles, transmit intervals, and environmental conditions.
• Sealed housing and valve hardware: Withstands centrifugal forces, moisture, and corrosion; service kits replace seals, cores, and caps during tire work.

These elements work together under strict power budgets: the sensor sleeps most of the time, wakes briefly to sample and transmit, then returns to a low-energy state.

How a Direct Sensor Communicates

From Sensing to the Dashboard

The data path from tire to instrument cluster is short but carefully managed to prioritize accuracy and battery life.

1. Wake and sample: The accelerometer or a timer wakes the sensor. It reads pressure and temperature and checks battery status.
2. Compensate and encode: The microcontroller applies calibration, temperature compensation, and diagnostic checks, then builds a data frame with a unique sensor ID and error detection (CRC).
3. Transmit: The sensor sends a short RF burst (often tens of milliseconds) on 315/433 MHz, or uses a BLE advertisement on 2.4 GHz for newer systems.
4. Vehicle reception: A receiver module or body control module collects packets from all sensors, filters duplicates, and validates IDs.
5. Evaluation: The TPMS logic compares reported pressures (temperature-compensated where applicable) to thresholds based on the vehicle’s door-jamb placard.
6. Alerting: If a tire is sufficiently low or a rapid deflation is detected, the instrument cluster illuminates the TPMS warning and may display per-tire values.

This cycle repeats more frequently while driving and far less often when parked, balancing responsiveness with battery longevity.

When and How Often Sensors Transmit

Transmission behavior adjusts to vehicle state and service operations, ensuring timely alerts without draining the battery.

• Driving: Many sensors transmit every 30–60 seconds at speed; under rapid pressure changes or high speeds, some increase rate.
• Stationary: Infrequent heartbeats (e.g., every 15–60 minutes) confirm sensor health; many go fully dormant after a time-out.
• Motion detection: An accelerometer or centrifugal switch wakes the sensor when the wheel starts turning.
• LF triggers: During service or relearn, the vehicle or a tool sends a low-frequency wake signal to prompt immediate identification and pairing.
• Spare tires: If equipped with a sensor, spares often transmit less frequently and may not be monitored until installed.

The exact cadence varies by manufacturer and sensor supplier, but it always aims to catch meaningful pressure changes quickly while preserving battery life.

How Indirect TPMS Infers Pressure

Indirect systems don’t read pressure directly; they watch how a tire’s effective rolling radius and vibration signature change as pressure drops. Lower pressure slightly reduces tire diameter, making that wheel turn faster than the others at the same vehicle speed.

• Wheel-speed comparison: The control unit compares rotational speeds across wheels to detect one tire spinning slightly faster—an underinflation hint.
• Spectral analysis: Algorithms examine resonance peaks in wheel-speed signals; underinflation shifts these characteristics.
• Model-based corrections: Some systems factor in load, temperature, and driving dynamics to reduce false alarms.

Indirect TPMS is lighter and cheaper and doesn’t need batteries in the wheel, but it usually requires driver calibration after setting pressures and can be slower to detect gradual leaks.

Why the TPMS Light Turns On

When thresholds are crossed or the system can’t read a sensor reliably, the dashboard warning appears. Knowing the meanings helps with quick diagnosis.

• Solid yellow TPMS icon: One or more tires is below the system’s threshold. In the U.S., regulations require a warning when a tire is at or below 25% under the placard pressure (or below a minimum baseline), and similar rules apply in the EU and other regions.
• Blinking icon for 60–90 seconds at startup, then solid: A system fault—such as a dead battery in a sensor, a missing sensor, or RF interference—followed by a general warning.
• Per-tire readouts: Vehicles that display individual pressures show which tire is low, aiding quick air-up or inspection.

Regardless of the display type, drivers should check all tires with a reliable gauge when the warning appears, as multiple tires may be low.

What Affects Readings and Alerts

Several environmental and maintenance factors influence TPMS behavior and what you see on the dashboard.

• Temperature swings: Pressure drops about 1 psi (≈0.07 bar) for every 10°F (≈5.6°C) decrease in temperature; cold snaps commonly trigger alerts.
• Altitude changes: Climbing to higher elevations reduces outside atmospheric pressure and can shift indicated readings; some systems compensate via temperature and learned baselines.
• Heat during driving: Tires warm up and pressures rise; always set pressures “cold” per the door placard before daily driving.
• Slow vs. rapid leaks: Nails or bead leaks may trigger gradual alerts; cuts or valve failures can prompt urgent warnings with faster chimes.
• Rotation and wheel swaps: Direct TPMS often needs a relearn so the car knows each sensor’s new position; indirect systems require recalibration after any pressure change.
• Aftermarket wheels and stems: Use compatible clamp-in or snap-in sensors; metal stems require correct torque and fresh seals to prevent leaks and corrosion.
• Battery aging: Direct sensors typically last 5–10 years. As voltage drops, communication becomes intermittent before failing.

Understanding these influences helps distinguish normal seasonal changes from true leaks or system faults.

Maintenance and Troubleshooting Tips

Basic care keeps TPMS accurate and extends sensor life. Service procedures are specific but straightforward once you know what to check.

• Use the placard: Inflate to the values on the door-jamb placard, not the tire sidewall maximum.
• Measure cold: Check pressures before driving or after the car has been parked for several hours.
• Relearn or calibrate: After rotations or tire service, run the sensor relearn (direct TPMS) or calibration routine (indirect TPMS) per the owner’s manual.
• Service kits at tire changes: Replace valve cores, seals, and caps; torque clamp-in stems to spec to prevent leaks.
• Sensor batteries: When one dies, consider replacing all sensors if they’re of similar age to avoid repeated labor.
• OBD/scan tools: TPMS tools can trigger LF wake-ups, read sensor IDs and pressures, and help diagnose RF interference or ID mismatches.
• ID cloning for winter wheels: Aftermarket sensors can clone IDs to avoid an OBD relearn on some vehicles.
• BLE pairing: On newer BLE-based systems (e.g., several EVs), follow on-screen prompts or service procedures to pair sensors; some can display richer data in apps.

Regular checks and proper service practices reduce nuisance warnings and ensure the system is ready to flag real problems.

The Regulatory Backdrop—and What’s Next

TPMS became mandatory on new light vehicles in the United States starting in 2007 following the TREAD Act; the European Union required TPMS on new passenger cars from 2014. These rules set performance thresholds and reliability expectations, not the specific technology. The industry is now gradually adopting BLE-based sensors on some platforms—especially EVs—to simplify pairing, improve data throughput, and enable smartphone integration. Expect incremental gains in accuracy, cybersecurity hardening, and diagnostics, but the core principle will remain: measure or infer pressure reliably, alert promptly, and conserve battery life in the wheel.

Summary

A tire pressure sensor either directly measures pressure and temperature in each wheel and transmits those readings wirelessly, or it infers low pressure from wheel-speed behavior without in-tire electronics. Direct TPMS uses a MEMS transducer, microcontroller, and RF/BLE link for accurate per-tire data; indirect TPMS leverages ABS sensors and algorithms with less hardware. Both aim to warn drivers quickly when underinflation threatens safety and efficiency. Keep pressures set to the placard values, perform relearns or calibrations after service, and address warnings promptly to extend tire life and maintain safe handling.

Why is my tire pressure light on when my tires are fine?

Your TPMS (Tire Pressure Monitoring System) light may be on even if your tires are fine due to a malfunctioning sensor, temperature fluctuations causing pressure changes, a low spare tire, or a need to reset the system after recent maintenance. To resolve the issue, you should first verify the pressure in all tires, including the spare, using a reliable gauge. If the pressure is correct, check your owner’s manual for the specific reset procedure for your vehicle; if that doesn’t work, a sensor issue or a problem with the TPMS control module requires a professional diagnostic and repair at a mechanic.
 
This video explains common reasons why the TPMS light stays on even if tires are fine: 58sFixITYouTube · Jan 18, 2025
Why the Light Stays On

• Malfunctioning TPMS Sensor: Opens in new tabSensors can wear out over time, have dead batteries, or be damaged from impacts like potholes or curbs, leading to incorrect pressure readings. 
• Temperature Fluctuations: Opens in new tabCold weather causes tire pressure to drop as the air contracts, which can trigger the light. 
• Low Spare Tire Pressure: Opens in new tabIf your vehicle has a TPMS sensor in the spare tire, a low-pressure spare will also illuminate the warning light. 
• Incorrect System Calibration: Opens in new tabAfter tire changes or rotations, the system may need to be manually recalibrated to recognize the new pressure readings. 
• Faulty TPMS Module: Opens in new tabThe central TPMS module can have electrical or software issues that cause it to report false warnings. 

What You Can Do

1. Check Tire Pressure: Using a reliable tire pressure gauge, check the pressure in all four tires and the spare tire. Ensure they are inflated to the manufacturer’s recommended PSI, which is typically found on a sticker on the driver’s side doorjamb. 
2. Drive for a Short Distance: Some TPMS systems may need to be driven for a few miles to reset after pressure changes. 
3. Reset the TPMS: Consult your owner’s manual for the specific steps to reset or recalibrate the system, as this varies by vehicle. 
4. Inspect for Interference: Unplug any devices from USB or 12-volt ports, as they can sometimes cause interference with the TPMS sensors. 

You can watch this video to learn how to reset the tire pressure indicator: 35sHondaYouTube · Jun 28, 2022
When to See a Mechanic
If you’ve confirmed the tire pressure is correct and the system doesn’t reset after driving, a professional diagnosis is needed. A mechanic can: 

• Use specialized equipment to test the TPMS sensors and identify any faulty units. 
• Scan the TPMS module to check for errors or required recalibration. 
• Replace any malfunctioning sensors or the control module itself. 

How do tire pressure sensors stay charged?

TPMS sensors stay charged using small, internal batteries that are sealed within the sensor. These batteries are not designed to be replaced and are expected to last for 5 to 10 years before needing the entire sensor to be replaced. The sensors use the energy from their batteries to periodically check tire pressure and send readings to the vehicle, but they enter a power-saving sleep mode when the vehicle is not moving.
 
How they are powered:

• Internal Batteries: Opens in new tabEach TPMS sensor contains a small, non-replaceable battery, typically a lithium-ion type. 
• Battery Life: Opens in new tabThese batteries are engineered to last several years, usually between 5 and 10 years, depending on usage and environmental conditions. 
• Sleep Mode: Opens in new tabTo conserve power, the sensors go into a low-power “sleep mode” when the vehicle is stationary, reducing battery consumption. 
• Transmission on Movement: Opens in new tabWhen the vehicle starts moving, the sensors activate and begin transmitting tire pressure and temperature data to the car’s computer. 

When batteries fail: 

• Battery Depletion: Opens in new tabOver time, the internal battery will eventually lose its charge, causing the sensor to fail.
• TPMS Light: Opens in new tabA low battery charge in a sensor will typically trigger the TPMS warning light on the vehicle’s instrument panel.
• Sensor Replacement: Opens in new tabBecause the batteries are sealed and non-replaceable, the entire TPMS sensor assembly must be replaced when the battery dies.

How do tire pressure sensors get power?

Tire pressure sensors are powered by small, long-lasting batteries sealed inside the sensor assembly. These batteries are not user-replaceable and are designed to power the sensor for the life of the component, typically 5 to 10 years, after which the entire sensor needs to be replaced.
 
This video explains how the battery is sealed inside the sensor and cannot be replaced: 59sHondaYouTube · Nov 4, 2014
How they get power:

• Internal Batteries: The most common method for direct TPMS is a small, self-contained battery, often a Lithium-ion battery. 
• Limited Life: These batteries are designed to last for a number of years, but they eventually lose their charge. 
• Sealed Design: The batteries are sealed within the sensor unit and cannot be replaced on their own. 
• Sensor Replacement: When the battery runs out, the entire sensor assembly must be replaced to keep the system functional. 

Factors influencing battery life:

• Driving Conditions: How often the sensor is activated and the overall driving conditions, such as temperature extremes, can affect how long the battery lasts. 
• Sleep Mode: To conserve battery power, the sensors often go into a sleep mode when the vehicle is not moving, but may periodically check in to send data. 

You can watch this video to learn more about factors influencing battery life: 58sCars SimplifiedYouTube · Aug 4, 2018
Indirect TPMS:

• Some vehicles use an Indirect TPMS, which does not have its own power source. 
• Instead, it relies on the vehicle’s existing Anti-lock Braking System (ABS) wheel speed sensors to monitor tire rotation. 
• The computer detects an underinflated tire by comparing wheel speeds and uses this information to trigger the warning light. 

How does a tire pressure sensor communicate with a car?

Tire pressure sensors communicate with a car’s computer wirelessly using radio frequency (RF) signals. These battery-powered sensors, mounted inside each wheel, continuously monitor tire pressure and temperature, transmitting data to an antenna on the vehicle’s body when a low pressure threshold is detected. The antenna relays this information to the car’s onboard computer, which then activates a warning light or message on the dashboard to alert the driver. 
This video explains the basics of how direct TPMS works: 47sCars SimplifiedYouTube · Apr 9, 2022
Here’s a step-by-step breakdown of the communication process:

1. Monitoring: Each tire pressure sensor internally measures the air pressure and temperature within its tire. 
2. Power Source: A small, long-life battery within the sensor powers its operations. 
3. Wireless Transmission: The sensor, acting as a tiny radio transmitter, sends a radio frequency (RF) signal to the vehicle’s receiving antenna. 
4. Antenna Reception: The antenna, often shared with the keyless entry system, receives the signal from the sensor. 
5. Data Relay: The received data is then sent to the car’s computer (ECU). 
6. Dashboard Alert: The ECU processes this information and activates a warning light or displays a message in the instrument cluster, indicating a potential issue with tire pressure. 
7. Sleep Mode: To conserve battery life, sensors enter a sleep mode when the vehicle is stationary and periodic data transmission ceases. They activate to send information when a low-pressure condition is detected or when the vehicle is in motion.