The Tire Pressure Monitoring System (TPMS) is a crucial safety feature in modern vehicles, designed to alert drivers when one or more tires are significantly underinflated. This can lead to unsafe driving conditions, increased fuel consumption, and premature tire wear. Understanding the working principle of TPMS sensors is essential for maintaining the safety and performance of your vehicle.
Direct TPMS
Direct TPMS utilizes pressure monitoring sensors installed within each tire to measure the specific pressure levels. These sensors are typically located on the valve stem and transmit the data wirelessly to a centralized control module. The module analyzes the information and sends alerts to the dashboard if the tire pressure falls below the recommended levels.
Technical Specifications of Direct TPMS Sensors
- Pressure Range: Direct TPMS sensors typically operate within a pressure range of 28-35 pounds per square inch (psi).
- Pressure Accuracy: These sensors can provide real-time pressure readings with an accuracy of ±1 psi.
- Temperature Monitoring: In addition to pressure, direct TPMS sensors can also measure and transmit tire temperature data.
- Wireless Transmission: The sensors use radio frequency (RF) signals to communicate with the vehicle’s control module, with each sensor having a unique serial number to ensure accurate identification.
- Battery Life: The batteries inside direct TPMS sensors are designed to last for approximately 10 years, reducing the need for frequent replacements.
Advantages of Direct TPMS
- Accurate Tire Pressure Readings: Direct TPMS provides actual pressure measurements from inside the tire, ensuring more accurate and reliable data compared to indirect systems.
- Resistance to Inaccuracies: Direct TPMS is not prone to inaccuracies caused by tire rotations or replacements, as the sensors are directly integrated with the tires.
- Simplified Resynchronization: After a tire rotation or replacement, direct TPMS sensors can be easily resynchronized with the vehicle’s control module, requiring less maintenance.
- Spare Tire Integration: Some vehicles may include direct TPMS sensors in the spare tire, providing comprehensive tire pressure monitoring.
Disadvantages of Direct TPMS
- Higher Cost: Direct TPMS systems are generally more expensive to install and maintain compared to indirect TPMS.
- Resynchronization Challenges: While simple, the resynchronization process may require specialized tools, which can be costly for consumers and auto shops.
- Non-Serviceable Batteries: The batteries in direct TPMS sensors are typically not serviceable, meaning the entire sensor must be replaced when the battery is drained.
- Proprietary Systems: The proprietary nature of some direct TPMS systems can make installation, service, and replacement more complex and confusing for both consumers and auto technicians.
- Sensor Susceptibility: Direct TPMS sensors are more susceptible to damage during the tire mounting and demounting process.
Indirect TPMS
Indirect TPMS, on the other hand, relies on the wheel speed sensors that are already part of the vehicle’s anti-lock braking system (ABS). These sensors measure the rate of revolution of each wheel and compare it to other vehicle operation data. When a wheel starts spinning faster than expected, the computer calculates that the tire is underinflated and triggers an alert to the driver.
Technical Specifications of Indirect TPMS
- Wheel Speed Sensors: Indirect TPMS utilizes the existing wheel speed sensors in the ABS system to detect changes in tire rotation rates.
- Underinflation Detection: The vehicle’s computer analyzes the wheel speed data and identifies when a tire is spinning faster than expected, indicating underinflation.
Advantages of Indirect TPMS
- Lower Cost: Indirect TPMS systems are generally less expensive to install and maintain compared to direct TPMS.
- Reduced Maintenance: Indirect TPMS requires less programming and maintenance over the years compared to direct TPMS.
- Simpler Installation: The overall installation and maintenance of indirect TPMS is less complex than its direct counterpart.
Disadvantages of Indirect TPMS
- Inaccuracy with Tire Changes: Indirect TPMS may become inaccurate if the vehicle is equipped with tires of a different size than the original equipment.
- Unreliability with Uneven Wear: Indirect TPMS can be unreliable when the tires are unevenly worn, as the wheel speed data may not accurately reflect underinflation.
- Mandatory Resets: Indirect TPMS systems must be reset after properly inflating each tire and after routine tire rotations.
Wireless Transmission in Direct TPMS
Direct TPMS sensors transmit the tire pressure and temperature data wirelessly to the vehicle’s control module using radio frequency (RF) signals. Each sensor has a unique serial number, which allows the system to distinguish between sensors and ignore signals from other vehicles in the vicinity.
Safety and Regulations
TPMS systems have become mandatory in many countries to improve road safety. In the United States, all vehicles manufactured after 2007 are required to be equipped with TPMS. Similarly, in the United Kingdom, all new cars manufactured after 2014 must be fitted with TPMS, and any vehicle with a faulty or inoperative system will fail its MOT (Ministry of Transport) test.
DIY and Maintenance
- Direct TPMS sensors generally require less maintenance compared to indirect TPMS, but the sensors may need to be replaced if the battery is drained.
- Indirect TPMS systems require periodic resets after tire maintenance, such as inflation or rotation.
- It is recommended to consult a local garage or automotive specialist for guidance on specific TPMS battery replacement and maintenance procedures.
Reference:
- https://www.bridgestonetire.com/learn/maintenance/tire-pressure-monitoring-system-how-tpms-works/
- https://www.reddit.com/r/explainlikeimfive/comments/w1o3bk/eli5_how_do_vehicle_tire_pressure_sensors_work/
- https://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/tire-pressure-monitoring-systems.htm
- https://www.goodyear.eu/en_gb/consumer/learn/what-is-tpms.html
- https://www.youtube.com/watch?v=bOLuRJaQIeI