What a TPMS warning light tells you
A TPMS warning light (Tire Pressure Monitoring System) appears on your dashboard when at least one tire is underinflated or when the system itself has detected a problem. The light usually looks like a tire with an exclamation mark inside it. When it comes on, one or more of your tires is likely below the pressure your vehicle manufacturer recommends — not the pressure printed on the tire sidewall, but the pressure listed on a sticker inside your driver's door jamb or in your owner's manual.
The system works through sensors mounted inside or on each tire that measure air pressure in real time. If pressure drops below a certain threshold (usually about 25% below the recommended level), the sensor sends a signal to your vehicle's computer, which triggers the warning light. This is a safety feature: underinflated tires wear faster, reduce fuel economy, and can overheat on long drives.
Key Takeaways
- Check the tire pressure sticker on your driver's door jamb to find the correct PSI for your vehicle, not the number on the tire sidewall.
- Use a tire pressure gauge to measure each tire's pressure when the tires are cold — before driving or at least three hours after driving.
- Add air at a gas station pump or tire shop until each tire reaches the recommended PSI, then recheck after a few minutes to confirm.
- If the warning light returns after you inflate the tires, one of your TPMS sensors may be faulty and need replacement.
- Temperature changes cause pressure to drop naturally — expect the light to come on in fall and winter as outside air cools.
Finding the correct tire pressure for your vehicle
The correct 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 vehicle needs. Instead, look for a sticker on the inside of your driver's door jamb, on the door edge itself, or in your owner's manual. This sticker lists the recommended PSI (pounds per square inch) for your front and rear tires — they may differ.
Write down this number before you check your tires. You will need it to know whether your current pressure is too low. Most vehicles recommend between 30 and 35 PSI, but some trucks and SUVs run higher. The sticker also lists the tire size and load capacity, which can be useful if you ever need to replace a tire.
How to check tire pressure yourself
You will need a tire pressure gauge, which costs between $5 and $20 and is available at any auto parts store, gas station, or online. The most common type is a pen-shaped dial gauge or a digital gauge with a small screen. Both work well. You also need to check your tires when they are cold — meaning before you drive for the day, or at least three hours after driving. Tire pressure rises as the tire heats up from friction, so a warm tire will give you a false high reading.
Remove the valve cap from the first tire (it usually twists off). Press the gauge firmly onto the valve stem until you hear a small hiss of air. Hold it steady for a second or two. The gauge will display the current pressure. Write it down. Repeat this for all four tires, including the spare if your vehicle has a TPMS sensor in it (some do, some do not). Compare each reading to the recommended PSI on your door jamb sticker.
Adding air to underinflated tires
If any tire is below the recommended pressure, you need to add air. Most gas stations have an air pump near the fuel pumps — some are free, and some charge 50 cents to $2. Tire shops and many car washes also have pumps. Drive to the pump and park so the valve stem is accessible. Remove the valve cap and attach the pump nozzle firmly to the stem.
Most pumps have a dial or digital display showing the current pressure. Set the target pressure to the recommended PSI from your door jamb sticker, and the pump will stop automatically when that pressure is reached. If your pump does not have an auto-stop feature, add air in short bursts — two to three seconds at a time — and check the pressure with your gauge between bursts. It is easier to add air than to let it out. Once you reach the target pressure, remove the pump, replace the valve cap, and move to the next tire.
After inflating all tires, wait a few minutes and recheck the pressure with your gauge. Pressure can fluctuate slightly during the inflation process, and you want to confirm that each tire settled at the correct level.
Why the warning light stays on after you inflate
If you have inflated all four tires to the correct pressure and the warning light is still on, one of your TPMS sensors is likely faulty or has a dead battery. TPMS sensors are small electronic devices that run on batteries lasting roughly 5 to 10 years. When a sensor battery dies or the sensor itself fails, it stops sending pressure data to your vehicle's computer, and the light stays on.
A faulty sensor does not affect your ability to drive safely — you can still check your tire pressure manually with a gauge. However, you lose the automatic warning system. A tire shop can diagnose which sensor is faulty using a TPMS scanner, and replacement usually costs between $50 and $200 per sensor depending on your vehicle. Some shops can reprogram a sensor; others need to replace it entirely.
Temperature changes and seasonal TPMS warnings
Tire pressure drops naturally as outside temperature falls. For every 10-degree Fahrenheit drop in temperature, tire pressure decreases by about 1 PSI. This means the warning light often comes on in fall and early winter even if your tires were properly inflated in summer. This is normal and expected. Check your tire pressure and add air as needed when the seasons change.
Conversely, pressure rises in summer heat. If you inflate your tires in winter and then drive in hot weather, the pressure may rise above the recommended level. This is less of a safety concern than underinflation, but overinflated tires can wear unevenly. Check pressure again when the weather warms up and let out a small amount of air if needed.
When to see a tire professional
Visit a tire shop or mechanic if you cannot locate the correct pressure information on your vehicle, if you inflate your tires and the light returns within a few days, or if you suspect a slow leak. A slow leak means air is escaping from the tire, and you will need to find and repair the source — usually a puncture, a faulty valve stem, or a bead leak where the tire meets the rim.
A professional can use a TPMS diagnostic tool to identify which sensor is faulty, check for leaks by submerging the tire in water, and replace sensors or repair leaks as needed. If multiple sensors are failing at once, it may indicate a larger electrical problem with your vehicle's TPMS system, which a mechanic should investigate.
Frequently Asked Questions
Can I drive with the TPMS light on?
Yes, the light itself is not a safety emergency. However, it signals that at least one tire is underinflated, which increases tire wear and reduces fuel economy. Check and inflate your tires as soon as you can. Driving on a significantly underinflated tire for a long distance can cause the tire to overheat and fail.
What if only one tire is low?
One low tire usually means a slow leak in that specific tire. Inflate it to the correct pressure and monitor it over the next few days. If the pressure drops again, the tire has a leak and needs repair or replacement. A tire shop can locate the leak by submerging the tire in water to find the puncture.
Do I need to replace all four TPMS sensors at once?
No. Replace only the sensor that is faulty. However, if all four sensors are the same age and approaching the end of their battery life, a shop may recommend replacing all four at once to avoid repeat visits. Ask the shop which sensors are failing and which are still working before deciding.
Is the number on the tire sidewall ever the correct pressure?
No. The sidewall number is the maximum pressure the tire can hold safely, not the pressure your vehicle manufacturer recommends. Always use the pressure listed on the sticker inside your driver's door jamb or in your owner's manual.
Why does my TPMS light come on only in winter?
Cold air causes tire pressure to drop naturally. As outside temperature falls, the air inside your tires contracts and pressure decreases. This is why the light often appears in fall and winter. Check your tire pressure and add air as needed when temperatures drop.