TPMS - Tire Pressure Monitoring System
Learn what a TPMS does, how it works, and why it makes your life better!
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What Is Important to Know about TPMS
In this article, you’ll learn what a TPMS is, how it works, the benefits TPMS provides you, TPMS meaning, and what to do when your vehicle’s TPMS light comes on.
TPMS is mandatory now in many countries and regions, including the U.S., Europe, and South Korea. Not only have these systems greatly increased vehicle safety, but they have provided cost savings too! When the TPMS light (which can be a message, image, or combo) comes on - what do you do?
Read on to learn how a TPMS works and what to do when you get a warning message in your car. You can also see a video episode on TPMS and tire inflation by visiting our video’s link at the end of this page.
What Is TPMS & What Does It Do?
TPMS is an abbreviation for “tire pressure monitoring system.” While TPMS may not make sense on its own, what the abbreviation stands for does! What this vehicle safety system does is accurately described by what it is called.
The TPMS monitors, in real-time, the air pressure in your vehicle’s tires. When the pressure in a tire declines to approximately 80% of the rated tire pressure, the tire sensors will send a signal to the system and trigger a dashboard alert that tire pressure is too low for a tire.
Depending on your vehicle year and model, the message may be only an icon, an icon along with a message, such as “Tire Pressure Low”, or an indicator telling which tire is low and by how much.
Like any warning light or message, it is a “call to action” to address the issue appropriately as soon as possible!
How Does TPMS Work?
There are two types of TPMS: direct and indirect. Intuitively, they are designated as dTPMS and iTPMS.
Direct TPMS Systems
Direct systems have a sensor in the tire, at the base of the tire stem. The sensor uses RF (radio frequency) to send a message to the monitoring system computer to tell the inflation condition of the tire. If pressures are adequate, no message is generated. If pressures are about 20% or lower than the specified pressure for that tire, then a low-pressure message is displayed.
Depending on the model and year of the vehicle, the message displayed may be a simple internationally used icon, or it may display “Low Tire Pressure” (or something similar), or it may tell you the position of the tire that is low (passenger front, spare, etc.).
Direct systems are more accurate, but more costly, as they have a sensor in each tire with limited battery life, and the batteries are sealed and not replaceable. When a sensor “dies”, the whole unit needs to be replaced. Fortunately, the battery life is between 5 and 10 years.
Indirect TPMS Systems
Indirect systems obtain data from the wheel speed sensors, as well as the ABS (Anti-lock braking) systems to estimate tire pressures. This is done using the rotational mass of the tire. The more air in the tire, the higher the rotational mass. Said another way, the system works well, but it is not as accurate as having a sensor in each tire.
Indirect systems are less expensive, at the cost of accuracy, and in some situations, will not trigger a warning if all the tires are running low (this can happen when the weather turns cold), as one of the ways this type of system works is by comparing rotational mass between the tires. If they are all about the same size, then no warning may occur.
Lastly, it’s not uncommon to have to reset the iTPMS system after every air refill for the tires.
What to Do When a TPMS Light Comes on
When a message or indicator activates on your dashboard telling you that you have low pressure in one of your tires, you need to take action - right away. Driving on an underinflated tire is not good.
Steps to take when a TPMS low tire pressure message comes on are:
Check the pressure on each tire to find if it is in range. While you’re at it, go ahead and “top-off” each tire to the correct pressure.
If you don’t have a spare, call for assistance. If you have a low tire, and the spare is flat, and you have no way to get the vehicle or tire to a repair facility, and you have no way to inflate the tire, then your options are very limited. After resolving to be better prepared next time, you will need to determine if the low tire has enough pressure to allow you to drive a short distance, at a very low speed to get it to an inflation station or repair facility. You will have to drive at a very low speed to assure you don’t destroy the tire by overheating or over flexing it. If at all possible, avoid this option. Get someone to come and help instead.
Check the pressure in the spare as well. The spare loses pressure over time and lets the system know it is low. Unless you eliminate the spare as the source of the low-pressure signal, you may cause yourself bigger problems than you need to.
Take the car on a test drive to reset the system if the pressure is okay. If all tires are inflated to specification, now take the car on a drive to reset the system. In most cases, the system will recalibrate after being driven over 20 mph (32 kph) for several minutes.
What to Do if the TPMS Is Still On after Inflating the Tires
You’ve checked all the tires, including the spare, and they are all inflated to specification. You’ve conducted your reset drive, and the low tire pressure message is still active. Now what? You now need to turn to professionals to help. The repairs at this point are likely beyond what can be done at home.
Some of the common reasons why the TPMS is still on after inflating the tires could include:
One of the tire sensors may be defective and has quit working.
TPMS tire sensors have approximately 10 years of battery life, but that varies. If you have older sensors, they simply may be running out of “juice.”
Corrosion around the valve stem may be affecting the sensor and has caused it to become inoperative.
The TPMS main system and the tire sensors may have stopped communicating, or the system has “lost track” of what sensors are where.
All of these situations can be addressed by a qualified tire dealer and service shop. If a new sensor is needed, or the system needs to be recalibrated, a special procedure, utilizing specialized (that means costly!) equipment for the TPMS main computer to “RELEARN” where the sensor is and its unique encoded signal.
A TPMS Reset Is NOT the Same as a RELEARN!
RELEARN is NOT the same thing as a RESET. A reset is when a sensor has read pressure as too low. Once the correct pressure is restored, and the sensor and system are subjected to a reset drive for several minutes over 20 mph (32 kph), it resets.
A “relearn” is needed after the replacement of tire sensors, when tires are rotated and put in different positions than they were before the rotation, or when a new set of tires are purchased and reinstalled on the vehicle.
Relearning requires equipment to communicate with the TPMS, including reading the encoded signals from each tire sensor. The RF signal is encoded so that your vehicle’s TPMS doesn’t read the sensors from other vehicle tires nearby. They are also encoded to address privacy concerns where locations of individual vehicles (and by extension - their occupants) could be determined by RF scanners and locators.
Relearning is also necessary to “tell” your car where each tire is located, such as driver front or back, passenger front or back, or spare. While some TPMS will simply display an icon or a generic message when one of the tires is low, some systems will display the tire location as well. This is not possible without the system “knowing” where each of the tires is.
Can You Do a TPMS Relearn Yourself?
Yes, you can, but you’ll need to determine if the special equipment and the learning curve are worth it. Full-service tire shops have commercial systems to conduct the relearn process.
There are handheld units available online to do this as well. The ones that we’ve seen are typically under $50, but you need to be sure to get the right one for your vehicle. These home mechanic types of models work only with the vehicle they are matched to (whereas commercial units are fully programmable to “play nice” with hundreds of models).
For as often as we would use it, and to learn the procedure, we think it’s better to have our local tire care partner take care of this. Of course, it’s your decision.
The handheld units work by “talking” to the TPMS module (while it is in “learn” mode) while holding the unit by each tire by the valve stem to identify the sensor inside and to tell the system it is operational and where on the vehicle it is located. The commercial units work on the same principle. Simple and effective.
Frequently Asked Questions
We’ve done our best to answer some of the most common questions about your vehicle’s TPMS here. If you have other tire pressure monitoring system questions, please leave them in the comments at the end of the article. We enjoy hearing from you and responding to your feedback!
Now, let’s get to our list of some of the most frequently asked questions about Tire Pressure Monitoring Systems!
What Does a TPMS Do and Why?
Tire Pressure Monitoring Systems do exactly that: monitor air pressures, in real-time on your vehicle - including the spare. When pressure reduces to about 80% of the recommended pressure, the system will generate a warning message on your dashboard.
Low tire pressure is not good. The sooner you know about it, the better. Underinflated tires are the cause of many accidents and fatalities. Even if you don’t have one of these events, tire life, handling characteristics, and fuel economy are all negatively affected.
Low tire pressures regularly cause catastrophic tire failure (tread delamination, “blow-outs”) due to the fatiguing of the tire sidewalls, bead, and tread.
For all these reasons, having a system that assists you in keeping your vehicle’s tires at the right inflation pressures is a good thing!
Do I Need to Check My Tire Pressure if My Car has TPMS?
You might be tempted to rely only on your vehicle TPMS to tell you when you need to inflate your tires - but that is a bad idea.
Since most TPMS won’t generate a warning until a tire is about 20% below the recommended pressure, regular tire pressure checks are called for. That 20% loss may not have dire results with injury (or worse yet, death), but that lower pressure really accelerates tire wear and decreases gas mileage.
The answer? Keep a good tire gauge on board, and check your tires every time you fuel up. Make that fuel you’re buying go further, and make the tires last longer, It’s a win-win.
How Do I Know What Pressure to Inflate My Tires to?
The most reliable way to know the pressure your tires will operate best is information readily shown on your vehicle itself. While the sidewall of your tires will show pressures for the tire, these are maximum pressures for that tire, not necessarily the optimum operating pressure.
If you inflate your tires to the max shown on the tires themselves, let’s say 40 PSI/276 kPa, they will still be rated to run safely. However, the ride may not be as comfortable, the contact patch of the tire (the amount of tread touching the road at any given time) may be too small, and the tire won’t be as flexible side to side, affecting handling characteristics.
So, get the pressure information from the factory label that is on the driver’s door edge. This is standard placement in the U.S. and Canada for this info. Use that, and you’re doing what is recommended for your vehicle.
What Are Some Most Common Reasons Tires Lose Pressure?
Tires lose pressure for a variety of reasons, some not so obvious! Tires, by their very nature, are slightly porous, so they will lose up to 10% pressure over a year, whether the vehicle is in use or not.
Spares are commonly overlooked when conducting pressure checks. Eventually, the pressure in the spare drops, triggering a low-pressure warning. Many vehicle owners have been stumped after checking the four main tires, inflating them correctly, and still experiencing a tire pressure low warning. Don’t forget the spare!
Another cause of leaks can be a failure of some type related to the valve stem. Corrosion where the stem goes through the wheel, or the internal components of the valve stem may fail.
Of course, tire damage, including punctures and side impacts (such as hitting a curb or parking bumper), are common culprits for losing tire pressure. While the TPMS tells you when pressures get low, it can’t tell you anything about the general condition of the tire, such as sidewall scuffs, tears, and damage. You need to do ongoing visual inspections to determine those and take the appropriate action.
Another commonly overlooked reason for tire pressure loss is the onset of cooler and cold weather. The reason is simple. Cold air is much denser than hot air. So, as temperatures drop, so does the density and related pressure in a tire. It takes more air to create the required pressure when it is cold than when it is hot.
So, that means when it cools down, you need to check your tires for underinflation. When it heats back up, you should check to assure your tires aren’t overinflated. These are small tasks to perform for your vehicle’s tires that work so hard for you!
Am I Required to Have a TPMS On My Passenger or Light Truck Vehicle?
It depends on where you are in the world. The United States was the first to require these systems to be factory installed (called OEM - Original Equipment Manufacturer) on all new cars beginning in 2007. Most of Europe did the same thing in 2012. South Korea went even further, requiring all cars to have them beginning in 2015. So, for older vehicles, after-market systems had to be installed.
Since different countries have varying policies, you’ll need to check with your local or national authorities, or at a trusted tire retailer.
Perhaps a better question is why you wouldn’t want this system installed in your vehicle? For all the benefits it provides, at a very reasonable cost of ownership, the system provides another layer of protection for safe driving.
Can I Buy TPMS Sensors and Install and Calibrate the Sensors Myself?
Like most items these days, you can purchase units online from a variety of sources, so yes, you can install them yourself. To do so, you’ll need some specialized tire and wheel-related equipment so as to unmount and mount tires, remove and reinstall valve stems, and inflate and balance the tires. There are some home garages that have this equipment, but not many. We find it easier to have our local tire retailer take care of all this for us. However, for those of you that have well-equipped garages, and love the satisfaction of caring extensively for your vehicle, there is no reason why this can’t be something you take on.
Are TPMS Systems Required on Commercial Trucks and Semis?
As of 2021, these systems are NOT required on light and heavy commercial vehicles, coaches, trailers, and buses in the U.S. and the U.K., but that is very likely to change soon. These systems are scheduled to be required in the U.K. sometime in 2022, and South Korea has already implemented a requirement for commercial vehicles. It’s likely the U.S. will follow suit in the not-too-distant future.
Even without a requirement in the U.S., many trucking firms have begun to make use of them for safety and economic reasons. Without an active monitoring system, it’s easy to have tires that become underinflated. In fact, the Federal Motor Carrier Safety Administration states, “About 1 out of 5 tractors/trucks is operating with one or more tires underinflated by at least 20 psi.”
Underinflated tires cost on many fronts. Fuel mileage is reduced due to the rolling resistance of underinflated tires. Braking, handling, traction, and cornering characteristics are all negatively affected when a tire’s pressure is too low. So, companies that have a fleet of trucks look for ways to boost safety and economy, and a TPMS is one way to address these issues.
Another is visual systems that are affixed to the valve stem. One such product is offered by Quick Pressure. Drivers can walk around their vehicles and look at the indicator on each valve stem. If the indicator shows green, it’s good. If red, the tire is at least 10 psi low.
Bottom Line
Tire Pressure Monitoring Systems (TPMS) have greatly increased safety with all vehicles where the system has been installed. Now mandatory in many major countries, benefits include better fuel economy, reduction of tire failures, better handling and braking characteristics, all the while reducing tire wear - meaning longer intervals between tire purchases.
TPMS should not be the only way that tire pressure and condition of the tires are monitored. Tires can be damaged and still hold air without being safe. Damage such as sidewall slices, hitting of deep ruts, potholes, curbs or parking stops can all cause damage that the TPMS may register or not.
TPMS also will not generate a “tire pressure low” message until there is approximately a 20% deficit, so it pays to check your tire pressure ongoing to get all that you can from your tires.
If you do have a message shown from the TPMS indicating tire pressure is low, you’ll need to assure all tires, including the spare, are filled to the pressure shown on the placard inside the driver door jamb. You will then need to drive the vehicle for several minutes to reset the sensor. If the message persists, take the vehicle to your tire service center to determine what the issue is and to get it resolved.
If you have any questions about tire pressure monitoring systems (TPMS) or want to share your knowledge on the topic, feel free to leave a message in the comments. We enjoy conversations with our readers!
