Tire Pressure and TPMS: What You Need to Know

Tire pressure can be one of the simplest but most overlooked parts of vehicle maintenance, yet is still very important. When your tires are under- or over-inflated, this can lead to poor gas mileage, uneven wear, and even blowouts. That’s why tire pressure monitoring systems (TPMS) have been required in all passenger vehicles under 10,000 pounds in the U.S. since 2008 (eCFR).

Here’s how tire pressure and TPMS work, how to check your pressure, and what to do when that dashboard warning light turns on.

What Is Tire Pressure?

Tire pressure is the amount of air inside your tires, measured in pounds per square inch (PSI). It keeps your tires structurally firm, the right shape, and able to support your vehicle on all types of terrain.

You’ll find the maximum PSI printed on the sidewall of the tires -- it's a legal requirement of all tires sold in the U.S. Don’t fill your tires to that number! Every car needs a different PSI, as the correct pressure factors in the weight and size of your vehicle, and the size of your wheels. Instead, check your owner's manual or the sticker inside the driver’s door to find the recommended PSI for your specific vehicle and tire setup.

How to Check Tire Pressure

To get an accurate tire pressure reading:

1. Wait until your car has been parked for at least three hours so tires are cold.
2. Use a tire pressure gauge (available at auto parts stores or gas stations).
3. Remove the valve cap, press the gauge onto the valve, and check the reading.
4. Record the PSI for each tire so you don’t mix them up.

Most cars should have their tire pressure checked once a month, according to tire manufacturers and NHTSA. It’s also a good idea to check it when the seasons change or there’s a significant drop in temperature. Cold air lowers PSI, and hot weather raises it, so it’s normal to see a change around 1 PSI for every 10 degree (F) change in temperature.

Don’t forget your spare tire. Many spares have a higher PSI than your regular tires, and you won’t want to be stuck with a flat and an unusable backup.

What Is TPMS and How Does It Work?

TPMS stands for tire pressure monitoring system. It’s an electronic system that alerts you when one or more tires drop below a safe PSI. When the system detects a low pressure or sensor issue, the TPMS warning light — a horseshoe shape with an exclamation mark — appears on your dashboard.

There are two types of TPMS: direct and indirect.

Direct TPMS (dTPMS)

The direct TPMS uses a small, battery-powered pressure sensor inside each tire, mounted to the wheel or attached to the valve stem. The sensor measures air pressure (and sometimes temperature) in real time and sends that data wirelessly to your vehicle’s computer using a radio frequency (RF) signal.

Each sensor has a unique ID, so the system can tell which tire the reading is coming from. If one or more tires drop at least 25% below the recommended PSI, the system triggers the TPMS warning light on your dashboard.

There are two types of direct systems:

• High Line TPMS: Displays the pressure reading for each individual tire on the dashboard. Some may show real-time updates or temperature.
• Low Line TPMS: Only activates the warning light when pressure is low. You’ll need to check each tire manually to find the issue.

Indirect TPMS (iTPMS)

An indirect TPMS doesn’t use tire sensors. Instead, it uses the ABS (anti-lock brake system) to monitor wheel speed. When a tire’s pressure drops, its diameter shrinks slightly, causing it to spin faster than the others. The system detects this imbalance, though it can also be affected by tire wear or https://www.tireagent.com/blog/mismatched-tires-different-brand-tires-on-car.

Indirect systems must be recalibrated when you change or rotate tires, or when tire pressure is adjusted.

How does TPMS know which tire is which?

In most direct TPMS systems, each sensor has a unique ID tied to a specific wheel location (front left, rear right, etc.). This mapping is either programmed at the factory, or the system learns it through a relearn procedure after tire rotations or sensor replacements. Some vehicles require a scan tool to manually assign sensor positions, while others relearn automatically after driving for a few miles.

What Does the TPMS Light Mean?

• Solid Light: One or more tires are at least 25% below the recommended pressure. Check and inflate your tires as soon as possible.
• Flashing Light: Typically, the light flashes for 60 to 90 seconds then stays solid. That signals there's a problem with the TPMS system itself, such as a dead sensor or battery. Visit a service center to have it inspected.

Changing Tires With TPMS

When you get new tires:

• Some direct TPMS systems will recalibrate automatically after driving a few miles. Others require a TPMS scan tool to register new sensor IDs. If the warning light stays on, return to your installer.
• Indirect TPMS systems must be manually reset, usually through your dashboard menu. Check your owner’s manual for instructions.

TPMS sensors in direct systems run on batteries that typically last 5 to 10 years. In snowy areas where road salt is common, the battery life can be shorter. Ask your mechanic to check the sensors when installing new tires or during routine maintenance. By the way, once a sensor's battery dies, the entire sensor must be replaced; they're not serviceable.

Final Tip: Which TPMS Do You Have?

How do you know which TPMS you have?

If your vehicle was built after 2008, it’s required by law to have a TPMS. Many 2007 models also include one, even though they weren’t yet required. To find out which type your car has, check the owner’s manual or search your vehicle's make and model online. look for the warning light when you turn the key to the “ON” position.

Whether you’re using a pressure gauge or relying on your TPMS, keeping your tires at the right PSI saves money, extends tire life, and keeps you safer on the road.

Tire Pressure and TPMS FAQs

How does a tire pressure sensor work?

The short answer for how TPMS works is: A tire pressure sensor is mounted on each of your car’s tires. A direct TPMS wirelessly sends a signal to your vehicle when tire pressure is low. An indirect tire pressure monitors wheel speed and detects tire pressure loss when one tire rotates faster than the others. 

What causes a TPMS light to come on?

The meaning of a solid TPMS light is low tire pressure. The meaning of a flashing light is a malfunction in the tire pressure monitoring system itself (dead TPMS battery, for example).  

Where can I check my tire pressure?

You can check tire pressure at a gas station or anywhere that has an air pump for filling tires (it's not unusual for these facilities to have broken gauges but working air pumps). Otherwise, you can try having your pressure checked at an auto parts store, but this isn’t always free. Alternatively, tire pressure gauges aren’t expensive; they run between $8 to $20. 

What is the average car tire pressure or PSI? What pressure should my tires be?

Most passenger vehicles recommend 32 to 35 PSI, regardless of size. Larger vehicles like trucks and SUVs may run higher if they use load-rated tires. Always check the sticker inside the driver’s door or your owner’s manual for the exact number.

Average car tire pressure depends on the size of the vehicle:

• Small cars (sedans): Around 30 to 35 PSI
• Larger cars (crossovers, hatchbacks, SUVs, light trucks): Around 32 to 35 PSI
• Electric vehicles: 38 to 45 PSI

Remember to check your vehicle’s specific required tire PSI on the inside sticker of your driver’s side door or in your owner’s manual. 

What’s the best PSI for car tires? 

The best PSI for car tires is the pressure recommended by the vehicle manufacturer, not the tire manufacturer. Tires only list max PSI, not the correct PSI. That information is found in your driver’s manual or on the sticker inside your driver’s side door. 

What’s the best PSI for SUV and pickup truck tires?

The best PSI for SUV and pickup truck tires is usually higher than that of a sedan or crossover, but it depends on the load rating of the tire and the tire type. Check your car’s manual and expect to have a higher PSI number. 

When is the best time to check tire pressure?

The best time to check your tire pressure is at least 3 hours after you’ve last driven, so your tires have a chance to settle and cool down. This will ensure you have the most accurate PSI rating and can fill them up correctly. 

How often do you need to check tire pressure?

We recommend checking your tire pressure around once a month and not waiting for your TPMS to alert you to low pressure. If the outside temperature drops or rises suddenly, you may want to give your tires a quick PSI check. 

What does it mean if my tire pressure light is blinking or flashing?

A flashing or blinking tire pressure light does not mean your tires have low pressure, but rather that there is an issue with the TPMS itself. The battery on the sensor may be dead, or the TPMS isn’t properly calibrated. Have it checked with a scan tool. 

What about when the tire pressure light keeps coming on and staying on?

If your tire pressure light is on in a solid light, it means that the TPMS monitoring your tire pressure has detected that one of your tires has low pressure. Check the pressure of each tire and compare it to the recommended PSI for your vehicle, found in your owner’s manual or on the inside sticker of the driver’s side door. Fill each tire to the recommended PSI and check again to see if the tire pressure light has turned off.

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