What a Tire Pressure Monitor System Does

A tire pressure monitor system (TPMS) is a set of sensors in or on your tires that measure air pressure and send readings to your vehicle's computer. When pressure in any tire drops below a threshold — usually about 25 percent below the manufacturer's recommended pressure — the system triggers a warning light on your dashboard. The light looks like a tire with an exclamation mark inside it.

TPMS became mandatory on all new vehicles sold in the United States starting in 2008. The system exists because underinflated tires wear faster, reduce fuel economy, and are more likely to fail suddenly. A working TPMS catches slow leaks you might not notice by touch or sight alone.

Your vehicle has either direct TPMS or indirect TPMS. Direct systems use actual pressure sensors mounted inside each tire or on the valve stem. Indirect systems use your existing wheel speed sensors (the ones that feed data to your anti-lock brakes) to detect when a tire is losing pressure by measuring how fast it spins compared to the others. Most vehicles made after 2010 use direct TPMS.

Key Takeaways

  • The TPMS warning light means at least one tire is underinflated, not that the system itself is broken.
  • Check all four tire pressures with a manual gauge as soon as the light comes on, because the system cannot tell you which tire is low.
  • Tire pressure changes with temperature, so the light may come on in cold weather even if your tires were properly inflated the day before.
  • Direct TPMS sensors have batteries that last 5 to 10 years and will eventually need replacement, which costs $15 to $60 per sensor depending on your vehicle.
  • A malfunctioning TPMS sensor or receiver will trigger a different warning light or message, usually labeled "TPMS fault" or "check TPMS system".

Why the Light Came On: Temperature and Pressure Changes

The most common reason the TPMS light comes on is a drop in outside temperature. Air contracts as it cools, so tire pressure falls roughly 1 pound per square inch (PSI) for every 10-degree Fahrenheit drop in temperature. If you live somewhere with cold winters, you may see the light come on overnight or during a cold snap, even though nothing is actually wrong with your tires.

Check your tire pressures with a manual tire gauge when the light first appears. You can find the correct pressure for your vehicle on a sticker inside the driver's door jamb or in your owner's manual — not on the tire sidewall itself, which lists the maximum pressure the tire can safely hold. If all four tires are within 2 to 3 PSI of the recommended pressure, temperature change is the culprit. Inflate them to the correct pressure and the light should turn off within a few driving cycles as the tires warm up.

If one tire is noticeably lower than the others, you have a slow leak. Proceed to the next section.

Checking Tire Pressure and Finding a Leak

You need a tire pressure gauge to see the actual readings. Digital gauges cost $10 to $25 and are easier to read than stick gauges. Most gas stations and tire shops have air pumps with built-in gauges you can use for free, though the accuracy varies.

Check all four tires when they are cold — meaning the vehicle has been parked for at least three hours or driven less than a mile at low speed. Tire pressure rises as you drive because friction heats the air inside, so a warm tire will read higher than its true pressure. Write down all four readings and compare them to the recommended pressure on your door jamb sticker.

If one tire is 5 to 10 PSI lower than the others, you likely have a slow leak. Inflate it to the correct pressure and monitor it over the next few days. If the pressure drops again, the tire has a puncture or a faulty valve stem. Take the vehicle to a tire shop for inspection. A small puncture in the tread can usually be patched for $10 to $25. If the leak is in the sidewall or the tire is too worn to patch, you will need a replacement.

If all four tires are equally low, the TPMS light came on because of temperature change, not a leak. Inflate all four to the correct pressure and the light should turn off.

Understanding Direct and Indirect TPMS Sensors

Direct TPMS uses small electronic sensors mounted inside each tire or clipped to the valve stem. Each sensor has a battery, a pressure transducer, and a radio transmitter. The sensors send pressure readings wirelessly to a receiver module in your vehicle about once per minute while you are driving. When a tire pressure drops below the warning threshold, the receiver triggers the dashboard light.

Direct sensors are more accurate than indirect systems but have a drawback: the batteries inside them last 5 to 10 years and cannot be replaced. Once a battery dies, the entire sensor must be replaced. Replacement costs range from $15 to $60 per sensor depending on your vehicle make and model, plus labor if you have a shop do it. Some vehicles charge $100 to $200 per sensor because the sensor is integrated into the wheel assembly.

Indirect TPMS does not use separate sensors. Instead, it monitors the wheel speed sensors that are already part of your anti-lock brake system. When one tire loses pressure, it becomes slightly smaller and spins faster than the others. The system detects this difference and triggers the warning light. Indirect TPMS is cheaper to maintain because there are no batteries to replace, but it cannot tell you the actual pressure in any tire — only that one is lower than the others. It also takes longer to detect a slow leak because the pressure change has to be large enough to affect wheel speed noticeably.

When the TPMS Light Stays On After Inflating

If you have inflated all four tires to the correct pressure and the light is still on, one of three things is happening: a sensor battery has died, a sensor is malfunctioning, or the receiver module in your vehicle is not working.

On vehicles with direct TPMS, a dead sensor battery will cause the light to stay on permanently. The vehicle's computer may also display a message like "TPMS sensor fault" or "check TPMS system" instead of the standard low-pressure warning. You will need to replace the faulty sensor. Visit a tire shop or dealership and tell them which tire position has the problem (driver front, passenger rear, and so on). They can test the sensors to confirm which one is dead and replace it.

On vehicles with indirect TPMS, a malfunctioning wheel speed sensor or a problem with the receiver module can cause a false warning. This is less common than a dead direct sensor battery. A scan tool is needed to diagnose the problem, so a tire shop or dealership will have to investigate. If the light comes on and stays on even though all tire pressures are correct and there is no visible damage, have the system scanned.

Resetting the TPMS Light After Repairs

After you have repaired a tire, replaced a sensor, or straightforward inflated underinflated tires, the warning light should turn off on its own within a few driving cycles — usually within 20 miles of highway driving. The vehicle's computer needs time to receive new pressure readings from all sensors and confirm that pressures are now within range.

Some vehicles have a TPMS reset button, usually located under the steering wheel or in the glove compartment. Consult your owner's manual to find it if you have one. Pressing the button tells the system to recalibrate and forget the old low-pressure reading. This is useful if you have just replaced a sensor or rotated your tires and the light is slow to turn off.

If the light does not turn off after 50 miles of normal driving and all tire pressures are correct, the system may have a fault. Have it scanned at a tire shop or dealership.

Tire Pressure and Seasonal Changes

Tire pressure changes with the seasons because air expands in heat and contracts in cold. In winter, you may see the TPMS light come on even though your tires were properly inflated in fall. In summer, the same tires may read 3 to 5 PSI higher than they did in winter.

The solution is to check and adjust tire pressure twice a year — once in fall before cold weather arrives, and once in spring as temperatures warm up. Inflate to the pressure listed on your door jamb sticker, not the maximum pressure on the tire sidewall. If you live in a place with extreme temperature swings, you may need to adjust more often.

Some drivers add a few extra PSI in winter to compensate for the expected pressure drop, but this is not necessary. The TPMS system is designed to handle normal seasonal variation. Overinflating tires reduces traction and causes uneven wear, so it is better to straightforward check pressure when the light comes on and adjust as needed.

Frequently Asked Questions

Can I drive with the TPMS light on?

You can drive short distances, but you should not ignore it. A significantly underinflated tire wears faster and can overheat, which increases the risk of a blowout. Check your tire pressures as soon as possible and inflate any that are low. If all pressures are correct and the light is still on, have the system scanned within a few days.

What if I cannot find the recommended tire pressure for my vehicle?

Look for a sticker on the inside of the driver's door jamb, the fuel door, or the glove compartment lid. If you cannot find it, check your owner's manual or search your vehicle's year, make, and model online. The tire shop where you buy air can also look it up for you. Do not use the pressure printed on the tire sidewall — that is the maximum pressure, not the recommended pressure.

Do I need to replace all four TPMS sensors at once?

No. Replace only the sensor that has failed. However, if your vehicle is older and multiple sensors are nearing the end of their battery life, a shop may recommend replacing all four at once to avoid repeat visits. Ask the shop which sensors tested as weak or failing before you decide.

Will the TPMS light come on if I use a tire plug or patch?

No, as long as the repair is done correctly and the tire holds pressure. The light comes on when pressure drops, not because of how the tire was repaired. After a plug or patch, inflate the tire to the correct pressure and the light should turn off within a few driving cycles.

What happens if my TPMS sensor gets damaged during a tire change?

If a tire shop damages a direct TPMS sensor while changing a tire, they are responsible for replacing it. Always tell the shop you have TPMS sensors before they begin work, and ask them to be careful around the valve stems or sensor mounting points. If a sensor is damaged, ask the shop to replace it and document the repair in writing.