What Is a TPMS and How Does It Work?

Today’s vehicles rely on countless systems to function, ranging from mechanical systems like your brakes to more elaborate computerized systems. Surprisingly, one of your car’s most sophisticated systems is its tire pressure monitoring system (TPMS) — the system responsible for activating the yellow light on your dashboard when your tires are low. Since 2007, almost every vehicle available for purchase in the U.S. has been legally required to incorporate some form of TPMS.

Many drivers don’t know how their car’s TPMS works, but these systems go a long way toward keeping you safe on the road. Keep reading for an in-depth overview of tire shop services and tire pressure monitoring systems from the basic principles behind these systems to how both of the leading TPMS varieties function.

TPMS 101

All kinds of factors can contribute to car accidents, including issues you may not have considered — and tire pressure definitely falls into this category. While driving with underinflated tires can be an easy problem to overlook, this is a more serious safety hazard than you might assume. Making matters worse, countless vehicles on the road have suboptimal tire pressure every day.

That’s where the TPMS comes in. As you may assume based on its name, your TPMS watches the tire pressure in each of your car’s wheels and informs you when these pressure levels are dangerously low. When it detects tire pressure issues, your TPMS will let you know about the problem by activating a specialized dashboard light. This yellow light is shaped like a cross-section of a tire with an exclamation point in the center.

How Your TPMS Works

To truly understand your TPMS’s inner workings, you’ll need to know a bit about the two main TPMS varieties on the market today: indirect and direct. 

Indirect TPMS

An indirect TPMS doesn’t technically measure your tire pressure at all. Instead, these systems utilize the same wheel speed sensors used in your anti-lock brake system. These sensors are designed to measure how fast each of your wheels is turning. Your onboard computer can analyze this information and compare it to other data points, such as your car’s overall speed.

When it knows how fast each of your wheels is supposed to rotate, your vehicle’s computer will know if one of your tires is spinning more quickly than it should be. If that happens, it will come to the conclusion that you have an underinflated tire and activate the corresponding warning light on your dashboard.

An indirect TPMS is typically cheaper and less maintenance-heavy than a direct TPMS. On the other hand, these systems may become inaccurate if you are dealing with uneven tire wear or buy tires that are bigger or smaller than your previous wheels. An indirect TPMS must also be reset whenever you rotate or inflate your tires.

Direct TPMS

Unlike indirect TPMSs, a direct TPMS can actively monitor your car’s tire pressure. To accomplish this, these systems utilize pressure monitoring sensors installed in each wheel, bypassing the need to estimate pressure levels based on wheel revolution readings. Some direct TPMSs can even measure each tire’s temperature.

The data collected by the direct sensor of a TPMS goes to a central control module. There, that information is analyzed, and if it points to tire inflation issues, this module will activate your TPMS dashboard light. Most TPMSs operate wirelessly; in these systems, sensors are distinguishable from each other and sensors on other cars thanks to their unique serial numbers.

It’s not hard to see why a direct TPMS is usually more accurate than an indirect TPMS. The process of recalibrating this system after a tire inflation or rotation is also simple (though it does rely on expensive tools). Furthermore, the batteries installed in direct TPMS sensors can last up to a decade.

Despite all these factors, a direct TPMS is not a “magic bullet” by any means — and not just because of their higher price tags. Many direct TPMSs are proprietary, meaning they can be tricky to install, repair, and replace for all but the most qualified auto shops. The sensors used in these systems can also be damaged during the mounting/demounting process. And while TPMS batteries are long-lasting, they usually aren’t replaceable; a dead sensor battery will typically require you to replace the entire sensor.

Get TPMS Service From a Qualified Fresno Tire Shop

As you can see, a direct TPMS needs careful attention to continue delivering the reliable results you count on. Meanwhile, indirect TPMSs should be maintained by professional Fresno tire mechanics to help them give the most accurate readings possible. Either way, you need a reliable Fresno tire shop to take care of your TPMS.

Whether your car uses a direct or indirect TPMS, Goodguys Tire & Automotive can keep this system in full working order! That’s because we employ ASE-certified mechanics — the most knowledgeable people working in the auto service industry. Our customers can also benefit from our great locations in the Fresno-Visalia area and online auto and tire repair coupons. 

If your TPMS needs attention, set up an appointment with Goodguys ASAP!