What Are TPMS Sensors? Understanding Tire Pressure Monitoring Systems

May 21, 2024


Tire Pressure Monitoring Systems (TPMS) are a vital safety feature in modern vehicles, designed to monitor the air pressure within pneumatic tires and notify the driver when the pressure falls below recommended levels. Understanding the types, functions and advantages of TPMS sensors can help drivers maintain optimal tire pressure and ensure driving safety and efficiency. In this article, we will explore what TPMS sensors are, how they work, and their importance in vehicle safety.


What is a TPMS sensor?

TPMS sensors are electronic devices installed in each tire of a vehicle to continuously monitor tire pressure. These sensors transmit real-time tire pressure information to the vehicle’s onboard computer system, which alerts the driver when any tire is significantly under-inflated.


5 Things You Didnt Know About TPMS


Types of TPMS sensors

There are two main types of TPMS sensors: direct TPMS and indirect TPMS.


1. Direct TPMS

  • Function: Direct TPMS sensors are located inside the tire, usually mounted on the rim. They measure the actual air pressure inside the tires and transmit this data to the vehicle’s computer.
  • Features:

a. Accurate real-time pressure readings.

b. Tire temperature can also be measured.

c. If tire pressure drops below recommended levels, an alert will sound immediately.

  • Advantage:

a. High precision and reliability.

b. Provides accurate pressure readings for each tire.

  • Disadvantages:

a. The cost is higher due to the complexity of the sensor.

b. Batteries or sensors need to be replaced regularly.



2. Indirect TPMS

  • Function: Indirect TPMS sensors do not directly measure tire pressure. Instead, they use the vehicle’s ABS (anti-lock braking system) sensors to monitor wheel speed. When a tire is underinflated, its diameter decreases, causing it to rotate faster than a properly inflated tire. The system detects differences in wheel speed and triggers an alarm.
  • Features:

a. No direct pressure measurement is made.

b. Relying on wheel speed data.

  • Advantage:

a. Compared with direct TPMS, the cost is lower.

b. No need to replace batteries.

  • Disadvantages:

a. Not as accurate as direct TPMS.

b. Specific pressure readings were not available.

c. Slow pressure leaks may not be detected.


How the TPMS sensor works

1. Direct TPMS operation

  • Sensor location: Direct TPMS sensors are mounted inside the tire, usually on the valve or attached to the rim.
  • Data transmission: These sensors measure the air pressure and temperature within the tires and transmit this information wirelessly to the vehicle’s TPMS control unit.
  • Driver Alert: When the air pressure in any tire falls below the manufacturer’s recommended level, the system triggers a warning light on the dashboard to remind the driver to check and inflate the tire.


2. Indirect TPMS Operation

  • Sensor Integration: Indirect TPMS uses existing ABS wheel speed sensors to monitor the rotational speed of each wheel.
  • Pressure Detection: The system detects if a tire is under-inflated by comparing the rotation speed of all four wheels (faster rotation speed indicates lower pressure).
  • Driver Alert: Similar to direct TPMS, when a significant wheel speed difference is detected, an alert is triggered on the dashboard indicating a possible under-inflation condition.






Benefits of TPMS Sensors

  • Safety: Maintaining proper tire pressure increases overall driving safety by reducing the risk of a puncture and improving vehicle handling.
  • Fuel Efficiency: Properly inflated tires reduce rolling resistance, which improves fuel efficiency and reduces fuel costs.
  • Tire life: Correct tire pressure helps prevent uneven tire wear and extends tire life.
  • Environmental Impact: Improved fuel efficiency and extended tire life help reduce a vehicle’s environmental footprint.


Common TPMS sensor issues

  • Sensor battery life: Batteries in direct TPMS sensors typically last 5-10 years. When the battery is depleted, the entire sensor may need to be replaced.
  • False Alarms: Both types of TPMS can sometimes issue false alarms due to sensor failure or rapid temperature changes.
  • Calibration Requirements: Indirect TPMS systems may require recalibration after tire rotations, replacements, or significant changes in tire pressure.



TPMS sensors are an essential component in modern vehicles and play a key role in keeping tires healthy and ensuring driver safety. By continuously monitoring tire pressure and providing timely alerts, these sensors help prevent accidents, improve fuel efficiency and extend tire life. Understanding the differences between direct TPMS and indirect TPMS can help vehicle owners make informed decisions about maintenance and sensor replacement. For high-quality TPMS sensors and components, visit DRex Electronics to learn more about how we can support your vehicle safety and performance needs.