What is TPMS and How Does it Work?

Tire pressure monitoring systems (TPMS) are a safety feature on most modern vehicles that use a combination of hardware and software to warn drivers when their tire pressure is 25 percent above or below the recommended pressure for that vehicle. Since 2008 in the United States, manufacturers have been legally obligated to install TPMS on all new cars and light trucks to reduce accidents caused by incorrect tire pressure. A TPMS let drivers know when their car’s tire pressure is low by activating an indicator light on the dashboard. This indicator light looks like a horseshoe with an exclamation point inside it (though it actually depicts the cross-section of a tire).

TPMS

How does TPMS work?

There are two main kinds of TPMS: direct and indirect. A direct TPMS measures tire pressure directly via a pressure sensor attached to the back of each tire’s valve. This sensor is battery powered and transmits data to the vehicle’s central computer. An indirect TPMS collects data from existing sensors, such as ABS and wheel speed sensors, which is then interpreted by software to infer the tire pressure. This kind of system makes use of the fact that low tires rotate at a different speed than correctly inflated ones. Either system will activate the tire pressure symbol on the dashboard when pressure falls significantly below the recommended pressure for the vehicle.

What does it mean when TPMS light comes on?

When the TPMS light is on, it most likely means the system is performing exactly as designed: alerting you that your tire pressure is outside the recommended range. You should manually check the tire with a gauge and inflate the tire to the manufacturer’s recommended level if the pressure is low.

If the light is on but you find that the tire pressure is correct, the system may be malfunctioning. Another possible sign of a bad sensor is a TPMS indicator light that blinks when you start your car and then remains on. Temperature can also affect tire pressure, so if the TPMS light is alternating on and off, it may be that excessive heat or cold is pushing the pressure beyond the recommended values.

Is it safe to drive with the TPMS light on?

If your TMPS light is on, you should always assume your tire is underinflated and check it as soon as possible. Underinflated tires do not perform correctly and can lead to blowouts, loss of control, and poor handling. They are the cause of thousands of accidents per year in the United States alone, so it’s an issue that shouldn’t be taken lightly. If you check your tire pressure and none of your tires are low, it may be okay to keep driving slowly and carefully with the TPMS light on, but you should fix the problem as quickly as possible at your nearest service shop.

How much does it cost to replace the tire pressure sensor?

A tire pressure sensor’s price tag will depend on your car model and the part it requires. It is generally necessary to replace the sensor and the batteries together—they are usually a single unit. For the part and labor, you can expect to pay anywhere from $75 per sensor to over $200, depending on your vehicle.

Is TPMS required when replacing tires?

Yes, TPMS have been a required safety feature (under the TREAD Act in the US) since 2008.

How do you fix a TPMS sensor without replacing it?

TPMS sensors most often need to be replaced because their batteries have reached the end of their 5- to 10-year lifespan, although they could be damaged sooner by road conditions. Most sensor models have built-in, non-replaceable batteries, so the only solution is to replace the whole sensor. In some instances, problems with the valve stem can be fixed without putting in a whole new sensor unit.

Tire pressure and safety

You should always try to keep your tires inflated to the pressure recommended by your vehicle manufacturer. When tires are operated at improper pressures, the tire’s sidewalls can flex and damage the belting structure in the tires. You will not be able to see this damage, which can increase over time. This is why you should maintain proper inflation pressure and try to avoid driving when the TPMS light is on. If you absolutely must drive a short distance on a tire with severely low pressure, drive very slowly and use extreme caution. The tire should be inflated or changed before driving anywhere.

FAQs

What is the recommended tire pressure?

Recommended tire pressure varies based on the make and model of your car. The specific number (measure in pounds per square inch—PSI) can be found in the car’s manual or on a placard on the driver’s doorjamb.

Will the TPMS light come on if tires are overinflated?

Under U.S. law, TPMS are not required to notify a driver of overinflated tires. However, most TPMS do.

What is the TPMS reset button?

The TPMS reset button, which is located underneath the steering wheel in most vehicles, resets the TPMS sensors or system when pressed. TPMS resets should be done by a tire professional.

How do you know if you have a bad TPMS sensor?

If you see that your tire is low or flat but the TPMS indicator light does not come on, chances are you have a faulty sensor. Conversely, if the light comes on but all tires have stable and correct pressure, this also may mean you have a bad sensor, especially if the light blinks when you first start the vehicle. Take your vehicle to a tire service professional to have them check the sensors.

Can I use my old TPMS on my new wheels?

In most cases, a TPMS can be transferred over to a new set of wheels. But before doing so, you should take into account the age of the sensors and the cost of potentially having to dismount and remount both sets of tires to switch over the sensors.

Nearest dealer

If you still have questions about your TPMS or suspect your system or tires are not functioning properly, get help from your nearest tire dealer so you can stay safe on the road