What is TPMS sensor and how it works

Tires are the single most important thing to road safety. Keeping them in great shape will ensure that you will have the best possible handling and braking, which translates into much better safety. And most tire-related accidents happen because of underinflated tires.

When the pressure in the tires is lower than the specified, the vehicle will be much less stable. Braking distances will also be longer, and the overall handling unresponsive. Luckily, modern cars come with tire pressure monitoring sensors (TPMS), which notify the driver when there is a loss of pressure in one of the tires.

Most TPMS systems use a simple warning light on the dashboard to give the drive indication that one of the tires isn’t inflated properly. Some systems will even provide the pressure in every tire, which helps drivers easily pinpoint which tire needs inflating.

Why TPMS Systems are Important?

Tire pressure sensors are required in every modern car sold from 2007 that weighs under 10,000 pounds. The U.S. Congress passed this law after more than 100 people lost their lives in the Ford Explorer and Firestone tires fiasco.

All of this happened during the 90s’ when TPMS systems were built only in high-end vehicles and supercars, such as the Porsche 959 and Chevrolet Corvette. At that time, these sensors were installed in sports cars because tire pressure is very important in how the car handles. Having them in the Porsche 959 and Corvette was done to notify the driver if it was dangerous to drive aggressively in the corners.

In other passenger cars, though, tire pressure sensors weren’t deemed necessary. Then, the Ford Explorer and Firestone drama happened. While developing the Explorer, Ford found out that the vehicle easily rolls over if the tires are inflated in the usual 28 psi to 35 psi range. To mitigate that, they recommended tire pressure of only 26 psi.

The problem arose when the pressure fell under that mark. Tires aren’t really designed to be driven at very low pressures. The air in the tires gives them structural rigidity, which is very important for keeping good contact with the road. In the case of the Explorer and its Firestone tires, the pressure would fall to dangerously low 22 psi to 24 psi.

When that happened, the tires began to disintegrate. More precisely, the tread of the tires started to completely fall off the tire. The worse thing was that this thing happened while driving at higher speeds. When the Firestone tires disintegrated, the vehicle would completely lose control.

To prevent this from happening in the future, every modern car must be equipped with a TPMS system.

How Does a TPMS System Provide the Information to the Driver?

There are two entirely different TPMS systems, each of them with its own advantages and disadvantages.

Direct TPMS Systems

The most prevalent system today is called a direct tire pressure monitoring system. Cars that are equipped with this system have tire sensors at each wheel, which then wirelessly provide information to the vehicle’s ECU. Usually, OEM sensors are installed into the tire, but TPMS sensors for aftermarket wheels might be installed outside the tire.

Modern tire sensors can provide very precise pressure readouts. Some sensors even provide temperature readings for an even better understanding of the state of the tire.

The driver gets the information from these sensors on the dashboard. In most cars, the tire pressure warning light will go off, indicating that one of the tires isn’t inflated properly. On some vehicles, the driver can monitor each tire individually and see the correct pressure.

The former system notifies the driver only when the tire pressure falls below a certain threshold. For most driving scenarios, this should be enough to keep the vehicle safe. The latter notifies the driver on very slight changes in pressure, thus increasing safety. In other words, if the pressure falls by 1 psi, the car won’t become unsafe, but it will lose some of its cornering performance.

With that said, this system also has some disadvantages, all related to tire sensors. First of all, these sensors have batteries that let them contact with the vehicle’s computer wirelessly. TPMS batteries last for 5-10 years. That is long, but the moment the battery dies, the system won’t provide correct measurements to the car’s computer unit. This might happen while on the road, which is certainly unwelcome. Tire sensor batteries are also not replaceable. Usually, you need to replace the whole unit.

Then, the sensors might also get damaged if the driver hits a curb. That’s especially true on aftermarket wheels, where the tire sensor is located on the outside. Replacing the sensors is also a costly procedure that you can’t really do on your own. Every car manufacturer uses different sensors for their vehicles, which means that you probably need to go to a certified dealership. On top of that, a technician must reprogram the new sensor, so the vehicle’s ECU recognizes it. In other words, the car should be connected to a laptop with certified software.

Indirect TPMS Systems

Indirect tire pressure monitoring systems don’t rely on sensors to obtain the data. Instead, they use information from other sensors built into the car, and then an algorithm calculates the tire pressure.

It sounds confusing, but in reality, it really works. These systems can calculate the right pressure reading only using the speed sensors in the car. If one of the tires is underinflated (or smaller), then the speed reading will be higher than with normally inflated tires.

This system doesn’t suffer from the disadvantages of direct TPMS systems. However, it has its own disadvantages that, in our opinion, are even worse. In indirect TPMS, the driver always needs to reset the system after each tire inflation. Most car owners forget to do that, especially when on the road. When that happens, the system will think that the tires are overinflated and will provide the driver with the wrong readings.