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A tire pressure monitoring system (TPMS) is an electronic system designed to monitor the air pressure inside pneumatic tires on various types of vehicles[8]. A TPMS reports real-time tire-pressure information to the driver, using either a gauge, a pictogram display, or a simple low-pressure warning light[6]. The goal of a TPMS is avoiding traffic accidents, poor fuel economy, and increased tire wear due to under-inflated tires through early recognition of a hazardous state of the tires[6].
TPMS can be divided into two different types – direct (dTPMS) and indirect (iTPMS)[6]. Each serves the same purpose but operates under different mechanics[8].
Direct TPMS uses pressure monitoring sensors within each tire that monitor specific pressure levels[1]. Sensors in a direct TPMS may even provide tire temperature readings[1][2]. The direct tire pressure monitoring system sends all of this data to a centralized control module where it's analyzed, interpreted, and, if tire pressure is lower than it should be, transmitted directly to your dashboard where the indicator light illuminates[1].
A direct TPMS sensor consists of the following main functions[6]:
- Pressure sensor
- Analog-digital converter
- Microcontroller
- System controller
- Oscillator
- Radio frequency transmitter
- Low frequency receiver
- Voltage regulator (battery management)
Most originally fitted dTPMS have the sensor mounted on the inside of the rim, and the batteries are not exchangeable[6]. To save energy and prolong battery life, many dTPMS sensors do not transmit information when parked or apply a more power-expensive two-way communication which enables wake-up of the sensor[6]. OEM auto dTPMS units need to recognize the sensor positions and must ignore the signals from other vehicles to work properly[6].
Aftermarket dTPMS units not only transmit while vehicles are moving or parked but also provide users with some advanced monitoring options including data logging and remote monitoring options[6]. They are available for all types of vehicles, from motorcycles to heavy equipment, and can monitor up to 64 tires at a time, which is important for commercial vehicles[6]. Many aftermarket dTPMS units do not require specialized tools to program or reset, making them much simpler to use[6].
Direct TPMS measures the pressure in each tire directly. It uses sensors within the tires that send data to a central computer, allowing for accurate readings and immediate alerts if the pressure drops below a safe threshold[8].
Indirect TPMS works by constantly checking wheel speed and making calculations based on it[2]. The system continuously monitors each tire's rotational speed[2]. If one tire spins faster than the others, it indicates under-inflation[2]. Your ABS uses data from the speed of your rotating tires to measure the tire's diameter[2]. When one tire's diameter gets smaller, this shows it has lower pressure, and the ABS detects this variation[2]. The Powertrain Control Module (PCM) or a dedicated control unit processes these speed signals to identify discrepancies indicating low tire pressure and sends the details to your vehicle's onboard computer[2].
An Indirect TPMS includes several components[2]:
- Wheel-Speed Sensors: Part of the ABS, these sensors measure each tire's rotation speed and send real-time data to the PCM or ECU.
- Electronic Control Unit (ECU): This mini-computer processes speed data from all four wheels, using algorithms to compare rotational speeds so it can tell if a tire is underinflated.
- Tire Pressure Warning Light: You'll find this light on the dashboard. It lights up when the ECU detects a tire pressure issue so you can check and correct your tire pressure.
Indirect TPMS works with your vehicle's Antilock Braking System (ABS) sensors to approximate tire pressure. By comparing the revolution rate between wheels, the system can infer when a tire's circumference changes due to low pressure, triggering an alert[8].
| Direct System | Indirect System | |
|---|---|---|
| Measurement | Measures the actual air pressure in each tire using a sensor mounted inside the tire[8]. | Estimates tire pressure by monitoring the speed of each wheel using the vehicle's Antilock Braking System (ABS)[8]. |
| Accuracy | Generally more accurate as it provides real-time, precise measurements of tire pressure[7]. | Less accurate, as it relies on wheel speed and can be influenced by factors other than tire pressure, such as road conditions[7]. |
| Alerts | Provides immediate alerts if the pressure drops below a safe threshold[8]. Can identify under-inflated tires and alert drivers to low tire pressure[7]. Some advanced systems will prompt users to check individual tire pressures from the dashboard[7]. | May be slower to respond than direct systems[9]. |
| Maintenance | Sensors have batteries that need to be replaced periodically (typically every 7-10 years)4. Requires re-synchronization of sensors when tires are rotated4. | Minimal maintenance, as there are no dedicated sensors inside the tires4. |
| Cost | Generally more expensive due to the cost of the sensors4. | Less expensive since it uses existing ABS wheel speed sensors4. |
| How it Works | A TPMS sensor is a device that monitors the air pressure in a vehicle's tires[7]. It is usually mounted on the inside of the tire and sends information to a receiver that is either built into the car or connected to it[7]. The receiver then displays the pressure readings for each tire on the car's dashboard[7]. | Indirect TPMS systems work interestingly – as these don't directly measure the tire's pressure but the rate of revolution of each wheel and compare it with all the other wheel's readings[7]. When one of the wheels spins faster than the others, the onboard computer system declares it underinflated and reflects that assessment in the indicator[7]. |
| Additional notes | Preferred by many because it can accurately report the pressures of each tire and usually will allow you to check the air pressure in each tire at any time you like from your driver's seat4. | Relies on a TPMS reset button to set a baseline to measure wheel speed against4. The reset button is pressed when the tires have been checked manually and pressurized to the proper amounts4. The system will trigger an alert when the wheel speed changes enough from the Baseline wheel speed set by the reset button4. |
- Enhanced Safety: Proper tire pressure is crucial for safe driving[8]. TPMS helps maintain correct tire pressure, reducing tire failure risk while driving, such as blowouts and flats[8].
- Improved Fuel Efficiency: Tires at correct pressure levels offer the optimal balance of resistance and performance, which can significantly improve your vehicle's fuel efficiency[8].
- Extended Tire Life: Maintaining optimal tire pressure ensures that tires wear more evenly, thus extending their life and reducing the frequency of tire replacements[8].
- Environmental Benefits: By optimizing fuel consumption and reducing tire wear, TPMS not only saves you on operating costs but also aids in reducing your ecological footprint[8].
Understanding its main components can help you appreciate how it works to keep you safe on the road[3].
Tire Pressure Sensors
- These small electronic devices are typically mounted inside each tire or attached to the valve stem[3]. They continuously measure both air pressure and temperature within the tire[3].
- The sensors wirelessly transmit this information to the TPMS control module, ensuring real-time monitoring[3].
TPMS Control Module
- This module acts as the brain of the TPMS[3]. It receives data from the tire pressure sensors, processes it, and checks if any tire's pressure is outside the manufacturer's recommended range[3].
- If a discrepancy is detected, the control module triggers a warning signal to inform the driver[3].
Receiver/Display Unit
- This component receives warning signals from the TPMS control module[3]. It is typically integrated into the vehicle's instrument cluster or dashboard display but can also be a standalone unit[3].
- The display unit presents tire pressure information and alerts in an easily understandable format[3].
Warning Indicators
- These can be visual (like a dashboard light) or audible (sound signals) alerts that notify the driver of low tire pressure or other related issues[3].
- Common indicators include warning lights, display messages, and audible alerts, helping ensure the driver is informed about tire conditions[3].
Wiring and Communication System
- This system connects all TPMS components through wiring and communication channels[3].
- It enables the wireless transmission of data from sensors to the control module and from the control module to the display unit, ensuring effective communication[3].
Here are the general steps to set up a TPMS:
1. Program the monitor to the tire pressure you normally run in your tires[5]. It is advised to follow the manufacturer's recommendation, which is printed on the wall of the tire[5].
2. Set the parameters for the TPMS to alert you[5]. For instance, you might set the low warning at 10% below your normal tire pressure, and the high warning at 25% above the normal tire pressure[5].
3. Screw a sensor onto each of the tire stems, and put the wireless monitor on the dashboard where you can see it[5].
If the TPMS light is blinking, it means that the sensors are malfunctioning[14]. If you've tried syncing your TPMS Sensors to your car on your own and they won't connect, it is recommended to take your car to a professional shop or dealership[10]. There could be a few things going on like a service mode that may need to be enabled in order to program them[10].
- Collisions[14]
- Potholes and Curbs[14]
- Corrosion from road salts[13]
- Sensor Battery Failure[14]
Tire Pressure Monitoring Systems (TPMS) play a vital role in modern vehicles by ensuring optimal tire pressure, enhancing safety, improving fuel efficiency, and extending tire life. Whether direct or indirect, TPMS helps drivers maintain their vehicle's performance and reduce environmental impact. Regular maintenance and prompt attention to TPMS alerts are essential for maximizing these benefits and ensuring a safe driving experience.
A good quality TPMS constantly monitors the air pressure and temperature in the tires and shows that to you on a digital display[5]. If either temperature or pressure goes out of normal range, an alarm and the digital monitor give you a clear warning, so you can pull over and check out what's going on[5].
TPMS Sensors are required on all vehicles 2008 or newer[10]. If you're buying new wheels, do not use the old sensors as they're probably worn and are not designed for the new wheels since every type of wheel is produced at a different thickness and weight[10].
TPMS sensor batteries typically last seven to ten years and eventually need replacement[4]. The sensor batteries typically need to be replaced about every 18 months[5].
When the TPMS warning lamp on the instrument panel illuminates while driving, it means that the system has detected at least one tire with a pressure below the accepted minimum psi for the vehicle[13].
If the light comes on, indicating insufficient tire pressure, you should inspect your tires and top it off with air if needed[14]. If the light still becomes a problem, you should take it to a professional auto repair shop, because it could be more than your tires themselves, but a sensor problem[14].
[1] https://www.bridgestonetire.com/learn/maintenance/tire-pressure-monitoring-system-how-tpms-works/
[2] https://www.utires.com/articles/from-sensor-to-dashboard-how-do-tire-pressure-sensors-work/
[3] https://www.keystonerv.com/owners/understanding-tire-pressure-monitoring-systems-tpms
[4] https://www.youtube.com/watch?v=Zpykub1MpUQ
[5] https://www.airgear.store/pages/newbies-guide-to-tpms
[6] https://en.wikipedia.org/wiki/Tire-pressure_monitoring_system
[7] https://www.tires-easy.com/blog/tpms-sensor-101/
[8] https://techtirerepairs.com/tire-pressure-monitoring-systems-tpms-explained-benefits-and-maintenance/
[9] https://www.bh-sens.com/en/service/tpms-info-training-videos/faq
[10] https://www.fitmentindustries.com/blogs/515/faq-tpms
[11] https://www.maxitpms.com/FAQs/index.jhtml
[12] https://www.tirerack.com/upgrade-garage/common-tpms-questions-answered
[13] https://aviondemand.com/insider/tpms-qa-common-questions-answers-tire-pressure-monitoring-systems/
[14] https://www.rockymountaincarcare.com/blog/common-faqs-about-the-tpms
[15] https://106sttire.com/blog/everything-you-ever-wanted-to-know-about-tmps-faq-about-tire-pressure-monitoring-systems
[16] https://www.discounttire.com/learn/tpms-info/tpms-facts
[17] https://mycardoeswhat.org/safety-features/tire-pressure-monitoring-system/
[18] https://www.standardbrand.com/media/1646/st10235idl-may14_jtf_id-locator.pdf
[19] https://www.nxp.com/assets/block-diagram/en/TirePressureMonitoringSystemsTPMS_TIRE-PRESSURE-MONITORING-SYSTEM-TPMS.pdf
[20] https://www.shutterstock.com/search/tire-pressure-sensor
[21] https://www.doityourself.com/forum/passenger-cars-mini-vans-suv-service-repairs-no-trucks/645448-tpms-some-trivia-questions-about-how-they-work-go-bad.html
[22] https://quizlet.com/570122035/suspension-and-steering-i-aut-121-chapter-114-tire-pressure-monitoring-systems-chapter-quiz-questions-flash-cards/
[23] https://www.tacomaworld.com/threads/tpms-sensor-questions.805247/
[24] https://quizlet.com/360820971/ch-110-tire-pressure-monitoring-systems-flash-cards/
[25] https://www.reddit.com/r/AskMechanics/comments/18jcina/question_on_tire_pressure_monitoring_systems_tpms/
[26] https://mechanics.stackexchange.com/questions/90647/after-market-tire-pressure-monitoring-system-question
[27] https://www.reddit.com/r/explainlikeimfive/comments/w1o3bk/eli5_how_do_vehicle_tire_pressure_sensors_work/
[28] https://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/tire-pressure-monitoring-systems.htm
[29] https://fcc.report/FCC-ID/2BBMK-MMS-TPMS-0036/6692020.pdf
[30] https://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=1108/mode=prod/prd1108.htm
[31] https://www.bridgestonetire.com/learn/maintenance/tpms-light-on/
[32] https://www.youtube.com/watch?v=l7Q2WrmcMRQ
[33] https://www.youtube.com/watch?v=GzQU6QcSJOs
