What a tire monitor does

A tire pressure monitoring system (TPMS) is a sensor in each of your tires that tracks air pressure and sends a warning to your dashboard when pressure drops too low. The system does not fix the problem — it only alerts you that one or more tires need attention. Most cars sold in the United States since 2007 have TPMS as standard equipment.

When tire pressure falls below a threshold (usually around 25% below the manufacturer's recommended pressure), the TPMS triggers a warning light on your dashboard. The light typically shows a tire with an exclamation mark. This gives you time to check your tires and add air before the low pressure causes damage or affects how your car handles.

TPMS exists because underinflated tires wear faster, reduce fuel economy, and can overheat in certain driving conditions. The system catches problems you might not notice by looking at your tires, since a tire can lose significant pressure without appearing obviously flat to the eye.

Key Takeaways

  • TPMS sensors in each tire monitor air pressure and alert your dashboard when pressure drops too low, but they do not inflate the tire.
  • The warning light turns on when pressure falls roughly 25% below what the manufacturer recommends for your specific vehicle.
  • Low tire pressure increases wear, reduces fuel economy, and can cause handling problems, so the alert gives you time to add air.
  • TPMS sensors have batteries that last 5 to 10 years and may need replacement when they fail or when you buy new tires.

Direct TPMS versus indirect TPMS

There are two types of TPMS, and they work in different ways. Direct TPMS uses a small sensor and transmitter mounted inside each tire (usually on the valve stem or the wheel rim). The sensor measures pressure directly and sends a radio signal to your car's computer. When pressure drops, the signal changes and the warning light comes on.

Indirect TPMS does not use individual tire sensors. Instead, it monitors the speed of each wheel using the same sensors that run your anti-lock braking system (ABS). A tire that is underinflated has a smaller diameter and spins faster than a properly inflated tire. The system detects this difference and alerts you. Indirect systems are cheaper to install but less precise because they cannot tell you which tire is low or by how much.

Most vehicles use direct TPMS because it is more reliable and gives clearer information. Luxury cars and some trucks may use indirect systems. Your owner's manual will tell you which type your car has.

When TPMS sensors need replacement

TPMS sensors contain small batteries that power the transmitter. These batteries typically last between 5 and 10 years, depending on how often the sensor transmits and the climate where you live. Once the battery dies, the sensor stops working and your warning light may stay on or fail to alert you when pressure actually drops.

You will also need to replace sensors when you buy new tires, because the old sensors are mounted on your old wheels. A tire shop can transfer sensors to new wheels if the old ones still work, but this costs money and takes time. Some shops include sensor replacement in the price of new tires; others charge separately (typically $15 to $25 per sensor).

If your TPMS warning light stays on even after you have checked all four tires and they are at the correct pressure, a sensor battery has likely died or a sensor has failed. A mechanic can diagnose which sensor is the problem and replace it. Replacement sensors cost between $50 and $150 per tire depending on your vehicle and whether you go to a dealership or an independent shop.

How to find your car's recommended tire pressure

TPMS alerts you when pressure drops too low, but it does not tell you what the correct pressure should be for your specific car. The recommended pressure is not the number printed on the tire itself — that number is the maximum pressure the tire can safely hold, not the pressure your car needs.

Find your car's recommended pressure on a sticker inside the driver's door jamb or in your owner's manual. The sticker usually lists two pressures: one for the front tires and one for the rear (many cars have different recommendations for each axle). Check your tire pressure when the tires are cold — before you have driven the car or at least three hours after driving — because pressure rises as tires heat up from friction.

You can check pressure yourself with an inexpensive tire gauge (digital or dial-style, both work fine) or have it checked free at most gas stations and tire shops. Add air at a gas station air pump or at a tire shop if any tire is below the recommended pressure.

What the TPMS warning light means

A solid TPMS warning light means at least one tire has lost pressure and needs air. Check all four tires with a gauge to see which one is low. Add air to bring it to the recommended pressure. If you cannot find a gauge or air pump, most tire shops will check and fill your tires for free or for a small fee.

A blinking TPMS light (flashing on and off) usually signals a sensor malfunction rather than low pressure. This can mean a sensor battery has died, a sensor is damaged, or there is a problem with the TPMS receiver in your car. A mechanic will need to diagnose the issue. Do not ignore a blinking light, because it means your TPMS is not working and you will not get an alert if a tire actually loses pressure.

In cold weather, tire pressure naturally drops as air contracts. You may see your TPMS warning light come on in winter even if you filled your tires in fall. This is normal. Check the pressure and add air if needed. The light should go off once the tires warm up or you add air to the correct level.

TPMS and tire maintenance

TPMS is a safety tool, but it is not a substitute for regular tire checks. The system alerts you when pressure drops significantly, but small pressure losses over time can still affect how your car handles and how long your tires last. Check your tire pressure manually once a month and before long trips, even if your TPMS light is not on.

Tire pressure changes with temperature and driving habits. A tire that is at the correct pressure today may be low next month if the weather has turned cold or if you have been driving mostly on highways (which heats tires and can cause slow leaks). Monthly checks catch these gradual changes before they become problems.

If your TPMS light comes on repeatedly for the same tire, that tire may have a slow leak. A tire shop can patch a small puncture or identify whether the leak is coming from the valve stem, the bead (where the tire meets the rim), or a hole in the tread. Fixing a leak is cheaper than replacing a tire that has worn unevenly due to low pressure.

Frequently Asked Questions

Can I drive with the TPMS warning light on?

You can drive a short distance to a tire shop or gas station to check and fill your tires, but do not ignore the light or drive long distances with low pressure. Underinflated tires overheat, wear unevenly, and can fail suddenly. If the light is blinking (indicating a sensor problem), you can drive normally, but have the sensor checked soon so you know your TPMS is working.

Why does my TPMS light come on in winter?

Cold air takes up less space than warm air, so tire pressure drops when the temperature falls. For every 10-degree drop in outside temperature, tire pressure can drop about 1 pound per square inch. Check your tire pressure in winter and add air if needed. The light should go off once pressure is back to the recommended level.

Do I need to replace TPMS sensors when I get new tires?

Not always. If your current sensors are working and less than 5 years old, a tire shop can move them to your new wheels. If the sensors are older or damaged, replacement is recommended. Ask the shop whether transfer or replacement is included in the tire price before you buy.

What does it cost to replace a TPMS sensor?

A single sensor replacement typically costs $50 to $150 depending on your vehicle and whether you go to a dealership or independent shop. Some tire shops include sensor replacement in the price of new tires. Always ask for the total cost upfront before work begins.

Can I turn off the TPMS warning light myself?

No. The light is controlled by your car's computer and turns off only when tire pressure returns to the correct level or when a sensor malfunction is fixed. Attempting to disable TPMS is illegal in most places because it removes a safety feature. If the light stays on after you have filled your tires, have a mechanic diagnose the problem.