Tire pressure monitoring systems constantly monitor your vehicle’s tire pressures and alert you in real-time if your tires are low. This means added safety for thousands of drivers around the world.

So, how do tire pressure monitors work? Why does TPMS exist?

The fact is most people ignore tire maintenance until they are on the side of the road waiting for a tow truck.

Maybe you are one of them?

If you are, listen up. Driving on underinflated tires reduces fuel efficiency, absolutely destroys handling, and greatly increases tire wear. 

Luckily for us, modern cars have built-in tire monitoring systems that warn drivers of low tire pressures before they cause damage, or worse.

It’s like having a tire watchdog that barks when your tires are low on air.

A growling tire pressure watchdog - jerrypetrillo.com
A growling tire pressure watchdog – jerrypetrillo.com

At this point, if you want to know how tire pressure monitors work, you’re in the right place, this article takes a deep dive into TPMS.

I’ll explain how tire pressure monitors work, the differences between direct and indirect TPMS, and how tire pressure sensors function.

Let’s get started!…

First, a Little TPMS History

Early publicly available design concepts for TPMS can be traced back to the late 1980s. The fundamental principle behind TPMS involves sensors mounted in each tire, continuously monitoring tire pressure. 

In an attempt to make roads safer, the US government enacted the “TREAD” Act in 2000. This act mandated that all new vehicles sold in the United States after September 2007 will have a tire pressure monitoring system installed.

In the early stages, TPMS primarily used direct systems with sensors inside of each tire. Later, more improved versions (in my opinion) incorporated indirect systems, which utilize wheel speed sensors incorporated into the ABS to measure tire pressure. This eliminates the need for individual sensors and greatly improves reliability.

It’s 2024, and at this point, pretty much all cars on the road have a tire pressure monitoring system installed.

How Do Tire Pressure Monitors Work?

A TPMS sensor is mounted on the inside of a wheel. It uses specialized sensors that measure tire pressure and transmit the reading to the tire monitoring computer.

These sensors are mounted on the back side of the valve stem and use radio frequency to transmit pressure readings to the central TPMS module, or (computer.)

These sensors send real-time data, alerting the driver via a warning light in the instrument cluster if any tire pressure falls below the recommended level.

Sounds pretty simple right?

These tire pressure innovations are a standard feature in modern vehicles, enhancing safety, fuel efficiency, and overall driving experience.

Using mainly a 315mhz or 415mhz radio signal to communicate requires a little power, these sensors have internal batteries that fail over time.

If you have a TPMS warning light on the dash and the system will not reset, one (or all) sensor may have a weak battery. 

How does a TPMS sensor work?

A Typical TPMS Sensor Mounted In a Car’s Wheel- jerrypetrillo.com
A Typical TPMS Sensor Mounted In a Car’s Wheel- jerrypetrillo.com

TPMS sensors continuously monitor the air pressure inside each specific tire via built-in sensors. Cars with internal sensors will always have four separate sensors, one in each wheel.

Now, keep in mind that some brands, such as Toyota also install a sensor in the spare tire.

Go ahead… ask me how I know this…

A Quick Story About Some TPMS Experence

I have a lot of first-hand experence with tire pressure monitoring systems. Like any other thing, it took some mistakes to learn common issues.

I chased the cause of a TPMS light for hours on a customer’s Toyota in the early days. I set pressures, scanned for codes, and did everything else I could think of to get the tire warning light off.

Eventually, I found the unexpected cause… The spare was low, setting the warning light. AHHHGGH!! 

Lesson learned, don’t forget the spare.

Moving On

These pressure sensors “wake up” when the wheels start rolling and begin to take internal pressure readings within each tire, transmitting this data to the vehicle’s onboard computer system.

Once “awake” these babies constantly report changes in tire pressures to the central module.

If the pressure drops below the specified threshold, the sensor tells the module, which triggers a warning light on the dashboard.

Then the module tells you by shining an annoying, (yet important) light in your face.

Direct TPMS vs. Indirect TPMS

Tire pressure monitoring systems can be categorized into two styles of technology, Direct, and indirect.

Direct systems: Sensors are mounted inside each tire. A separate control module collects pressure data from each sensor and turns on the pressure warning if things get hairy. 

Indirect systems: (The better of the two in my opinion) measure the slight wheel speed changes via the ABS wheel speed sensors.

If a tire is underinflated it will always affect the wheel speed, even in the slightest amount. These systems are sensitive enough to pick up these variations without needing individual sensors. 

In my opinion, indirect systems are superior, simply because fewer parts are involved. 

How does direct TPMS work?

As we discussed above, direct TPMS directly measures the air pressure inside each tire using pressure sensors mounted within the tire. This approach is more accurate, real-time data on tire pressures is transmitted as soon as those lazy sensors wake up. This enables precise monitoring and instant warnings of low-pressure.

How does indirect TPMS work?

Much different than direct TPMS, indirect systems monitor tire pressures by gauging and comparing the wheel speeds of the vehicle.

To put it in simple terms, when a tire is underinflated, its rolling radius decreases, resulting in a change in wheel speed.

WOW, science class wasn’t a complete waste after all. 

The system relies on wheel speed sensor data and is integrated with the ABS (antilock brake module) The module identifies these slight but real speed variations and alerts you, the driver about an underinflated tire.

In Layman’s Terms, The Difference Between Direct and Indirect TPMS

Simply put, direct TPMS uses actual sensors within each tire to measure pressure levels, while indirect TPMS relies on monitoring live wheel speed to calculate changes in tire pressure.

Why Are Tire Pressure Monitoring Systems Important?

A person waiting for a tow truck because they have a flat tire - jerrypetrillo.com
A person waiting for a tow truck because they have a flat tire – jerrypetrillo.com

Did you know that driving on a car tire that’s low on air can cause permanent damage to the tire? When tire pressures drop there is more stress on the sidewalls of your tires.

This creates heat and more friction between the road and your half-inflated car tire. In a short time, the sidewall begins to wear and a deep groove wears into the sidewall, making the tire junk.

It’s better to run over a nail and lose all the air in your tire quickly than it is to drive on a tire grossly underinflated.

The first tire can be plugged and last for a long time instead of the tire with sidewall damage due to slow deflation and continued driving.

Q&A

What are the main types of TPMS?

There are two main types of TPMS: direct tire pressure monitoring and indirect tire pressure monitoring.

Direct TPMS sensors are mounted inside the tire and measure the actual pressure, while indirect TPMS systems monitor tire pressure based on factors such as wheel speed.

How do tire pressure sensors work?

Tire pressure sensors work by constantly monitoring the air pressure inside the tires.

They can detect when the pressure drops below a certain level, and send a signal to the vehicle’s computer system, which can illuminate a warning light on the dashboard.

What are the benefits of having Tire Pressure Monitoring?

TPMS can help to improve safety by alerting drivers to low tire pressure. This can lead to reduced accidents and issues that arise from low tires.

It also helps to increase fuel efficiency and prolong tire life by ensuring that the tires are properly inflated at all times.

How does the TPMS warning light work?

The TPMS warning light is a dashboard indicator that illuminates when the tire pressure in one or more tires is significantly low.

It is typically triggered when the pressure drops below a certain threshold, indicating the need for a tire pressure check.

Can I reset the TPMS Light myself?

A person kneeling down to check their tires at their house - jerrypetrillo.com
A person kneeling down to check their tires at their house – jerrypetrillo.com

Depending on the vehicle, some TPMS systems allow for a manual reset using a TPMS reset button or through a series of steps in the driver information display.

However, if you’re unsure, it’s best to consult the vehicle’s manual or visit a tire shop for assistance.

Are Direct and Indirect Tire Pressure Accurate?

TPMS is pretty accurate, tests have been performed on TPMS systems with good results by AAA automotive engineers.

With that said, checking your tire pressures manually is always the way to ensure your tires are inflated properly.

Is It a Bad Idea To Drive With a TPMS Light On?

Driving with the TPMS warning light on isn’t the best idea. Be sure to check your tire pressure as soon as possible. 

How To Reset a TPMS System 

After your tire pressures are set properly you’ll need to reset the tire pressure monitoring system.

Some vehicles only require a short test drive while others need to be activated, sometimes by a mechanic. Check your owner’s manual or go to a mechanic if unsure. 

In many cases, there may be a button or a specific reset that needs to be activated before driving. This allows the system to “relearn” and start monitoring current pressure.

How Does Tire Balancing Affect Tire Pressure Monitors in Vehicles?

Tire pressure monitors in vehicles rely on accurate data to function properly, and car tire balance explained how imbalance can affect tire pressure. When tires are not balanced, it can lead to uneven wear and tear, causing fluctuations in tire pressure. Proper tire balancing ensures accurate tire pressure readings for the monitors.

Wrapping Up

Hopefully, you now have a better grasp of TPMS and how tire pressure monitoring systems work. Although these systems can be a pain to deal with when a light is on the dash, they are crucial to keeping you safe on the road.

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