Understanding Tire Pressure Monitoring Systems: What Is TPMS?

• What's the flat tire signal on the dashboard mean?
• What are tire pressure monitoring systems?
• How does a tire pressure sensor work?
• What should you know before change a tire wtih TPMS?

If you have a car built during or after 2008, you may have seen this icon pop up on your dashboard. This icon means that your Tire Pressure Monitor System, or TPMS, has sensed that one or more of your tires has air pressure (measured in PSI) below the recommended amount. This electronic system is designed to prevent accidents by notifying the driver when a tire or tires needs air. Because it’s considered a key safety feature, TPMS has been mandatory for all passenger vehicles in the US since 2008. 

A TPMS can function in a few different ways, and it’s important to know how your TPMS works, so you’re aware of how to maintain it and, in some situations, why it may not detect tire pressure loss. 

In this article, we’ll be going through everything there is to know about a TPMS, so you know what it means when that little icon lights up. 

How Do TPMS Work?

If the TPMS icon lights up, that means that an electronic system connected to your tires has detected a discrepancy in your tire pressure. This doesn’t always mean your tire has a leak or puncture, as it may have lost pressure over time to the point where the system has detected an issue. 

However, depending on your vehicle, you may have a Direct TPMS or an Indirect TPMS. So, what’s the difference?

Flashing vs solid TPMS

If your TPMS light is solid, that indicates an issue with your tire. Usually, it means one or more tires is at least 25% below the recommended tire pressure. If your TPMS light is flashing, that indicates a problem with the TPMS system, so it's time to visit the dealership.  

Direct TPMS (dTPMS)

A direct TPMS will have an electronic pressure gauge sensor on the rims of all four of your tires. If one or more of the tires has tire pressure below the recommended amount for your tires, your car’s computer will detect the discrepancy and activate the warning light. 

All dTPMS will have gauges attached to your rims, however the way that the system extrapolates the data is dependent on whether you have a High Line or Low Line System.

• High Line TPMS

A high line system will have an active monitor for the individual pressures of each of your tires. The high line system will periodically receive information from the electronic gauges on your tires while the vehicle is running. Each sensor will have a unique indicator, so you’ll know the current pressure of your tires. You know that a car has a high line system if you can view the PSI of each tire somewhere on the dashboard. This is the most expensive system that allows you to actively monitor your tire pressure.

• Low Line TPMS

Low line systems do not have active monitoring. Rather, they send tire pressure readings at regular, or random, intervals. If the system detects an issue, the low-pressure light will turn on. Depending on your low line system, it may take readings more frequently to account for sudden changes in temperatures. If you see the light turn on in a low line system, you’ll still need to get out of your car with a manual pressure gauge to check which tire is having an issue. 

Indirect TPMS (iTPMS)

An indirect TPMS is a cheaper option that works with your anti lock braking system (ABS). An ABS monitors your tire rotation speed so that the driver can maintain control in emergencies. An iTPMS doesn’t have sensors on the tires, instead working with the part of the ABS that senses tire rotation speed to check if there is a discrepancy. 

An indirect TPMS is like an investigator that cross-references your tire rotation data with your accelerometers to determine if there’s an issue. This works because low-pressure tires will be slightly smaller due to less air being inside. With a smaller diameter comes a slightly different wheel speed and the iTPMS kicks in, activating the icon on your dashboard.

An iTPMS will need to be re-calibrated if you get new tires or if the pressure changes for any reason. This system will also not work if all four of your tires lose pressure simultaneously, as the system looks for discrepancies between the rotations of the individual tires. 

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Do You Have Tire Pressure Sensors? 

We mentioned earlier that vehicles made after 2008 will have some sort of system, but it’s a bit more complicated than that.

In September of 2007, the National Highway Traffic Safety Administration enacted a law that all vehicles under 10,000 pounds had to have a TPMS, as low tire pressure is a potential safety concern. 

However, according to Schrader TPMS Solutions, 70% of new vehicles from Sept. 1, 2006, to August 31, 2007, had a pressure monitoring system. Beyond 2007, all new vehicles would require a system installed. 

You can check your owner's manual to see what type of TPMS you have. Your dashboard will also have the standard low tire pressure indicator if you have a system. You can look for it when you turn your key ignition to the “ON” position.

Changing Tires When You Have a TPMS 

If you get a new set of tires, you’re usually getting a set that has around the same pressure, size, and rotation speed as your previous set. However, you may still need to recalibrate your TPMS depending on what system you have. 

A direct TPMS is the easiest, as the computer will make the adjustments automatically after a few miles of driving. You may notice the low-pressure reading at first, but this will likely go away. If the light persists after a few minutes, there may be an issue with the tires or the system, and you’ll need to take it back to the installer you used. 

An indirect TPMS requires more calibration, as the system will have to be manually reset. You may be able to do this on the dashboard, but it will be specific to your vehicle. Consult your owner's manual if you know that you have an indirect TPMS. 

Replacing and Maintaining a TPMS

A TPMS will need to be monitored and checked up just like any other part of your car. A direct TPMS has sensors that run on batteries, which can corrode or run out of power over time. If you live in a snowy area with a lot of road salt, your TPMS battery life may be shorter than most. According to Redi-Sensor, TPMS batteries have a lifespan of somewhere between 5 and 10 years 

Because the sensors are inside the tire rim, it can be a pain to replace if you’re not regularly having them checked on during tire replacement or regular maintenance. Ask your mechanic to check on your TPMS when they’re replacing your tires, as it’ll save you money in the long run.

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