What a tire pressure monitoring system does and how to check it
Your tire pressure monitoring system (TPMS) is a dashboard warning light and a set of sensors that track air pressure in each tire. When pressure drops below a threshold — usually 25% below the vehicle's recommended cold tire pressure — the system triggers a warning light on your dashboard. The light looks like a tire with an exclamation mark inside it.
Checking your TPMS means two things: confirming the warning light works when it should, and understanding what the light means when it appears. Most vehicles have either direct TPMS (individual sensors in each tire) or indirect TPMS (sensors that read wheel speed and detect pressure loss through abnormal rotation). Both systems need periodic attention, though for different reasons.
Key Takeaways
- A TPMS warning light means at least one tire is underinflated by 25% or more from the manufacturer's recommended pressure, not that a tire is flat.
- Check your actual tire pressure with a manual gauge at a gas station or tire shop to confirm which tire is low, because the system only alerts you — it does not tell you which tire or by how much.
- The recommended tire pressure is printed on a sticker inside the driver's door jamb, not on the tire sidewall, which shows the maximum pressure the tire can hold.
- TPMS sensors in direct systems last 5 to 10 years and may need replacement if the warning light stays on after you have inflated all tires to the correct pressure.
- A TPMS warning light that flashes for a few seconds when you start the vehicle is normal; a light that stays on means a real pressure problem exists.
How to read the TPMS warning light on your dashboard
The TPMS warning light appears as a yellow or amber tire symbol with an exclamation mark. On some vehicles, the light blinks for a few seconds when you start the engine — this is a normal system check and does not indicate a problem. If the light stays on solid or comes on while driving, at least one tire has lost pressure.
The light does not tell you which tire is low or how much pressure it has lost. It only signals that the system has detected a pressure drop of 25% or more below the cold tire pressure listed on the door jamb sticker. A tire that is 20% low will not trigger the light, even though it should be inflated. This is why the TPMS is a safety net, not a substitute for checking pressure yourself.
Finding the correct tire pressure for your vehicle
The correct pressure for your vehicle is printed on a white or silver sticker on the inside of the driver's door jamb, near where the door latches. This sticker lists the pressure in pounds per square inch (PSI) for the front and rear tires, which may differ. The pressure on the tire sidewall — often 44 PSI or higher — is the maximum pressure the tire can safely hold, not the pressure you should use.
Check tire pressure when the tires 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 the tire heats up from driving, so a warm tire will read 3 to 5 PSI higher than the true cold pressure. If you must check after driving, note that the reading will be higher than the actual cold pressure.
Steps to check your actual tire pressure
You will need a tire pressure gauge, available at any gas station, tire shop, or auto parts store for $10 to $20. Digital gauges are easier to read than stick gauges, but both work. Remove the valve cap from one tire by turning it counterclockwise. Press the gauge firmly onto the valve stem until you hear a slight hiss — the gauge will display the pressure in PSI.
Write down the pressure for each tire, including the spare if your vehicle has a TPMS sensor in it. Compare each reading to the pressure listed on the door jamb sticker. If any tire is 3 PSI or more below the recommended pressure, inflate it at a gas station air pump or have a tire shop do it. If all tires are within 2 PSI of the recommended pressure and the warning light is still on, the TPMS sensor itself may be faulty.
What to do if the warning light stays on after inflating your tires
If you have inflated all tires to the correct cold pressure and the TPMS light remains on, one of three things is happening: a sensor battery has died, a sensor has failed, or the system's receiver module is not communicating with the sensors. Direct TPMS sensors contain batteries that last 5 to 10 years. When a battery dies, the sensor stops transmitting pressure data and the light stays on.
A tire shop can use a TPMS diagnostic tool to identify which sensor is not responding. Replacing a single sensor typically costs $50 to $150 per tire, depending on the vehicle and whether the shop reuses the valve stem or replaces the entire assembly. Some shops charge a diagnostic fee of $20 to $50 to identify the problem before quoting a repair price. If multiple sensors have failed or the receiver module is faulty, costs can reach $300 to $500.
Seasonal pressure changes and TPMS warnings
Tire pressure drops in cold weather because air contracts as temperature falls. For every 10 degrees Fahrenheit the temperature drops, tire pressure decreases by roughly 1 PSI. In winter, you may see the TPMS light come on even if you inflated your tires correctly in fall. This is not a sensor failure — it is a pressure drop caused by cold.
When temperatures drop, check your tire pressure and inflate as needed. When temperatures rise again in spring, check pressure again because it will have increased. This seasonal pattern is normal and does not mean your TPMS is malfunctioning. However, if the light comes on in warm weather and stays on after you have inflated the tires, a sensor or receiver issue is more likely.
Indirect TPMS systems and how they differ
Some vehicles, particularly older models and certain luxury brands, use indirect TPMS instead of direct sensors. Indirect systems do not have pressure sensors in the tires. Instead, they monitor wheel speed using the anti-lock brake system sensors. When a tire loses pressure, it becomes slightly smaller in diameter, causing it to rotate faster than the other tires. The system detects this speed difference and triggers the warning light.
Indirect TPMS is less precise than direct systems because it cannot measure actual pressure — it only detects relative speed changes. If you rotate your tires, the system may need to be reset or recalibrated so it learns the new wheel positions. Check your owner's manual for the reset procedure, which usually involves driving at a specific speed or using a menu on the dashboard. If the light stays on after a tire rotation and reset, a wheel speed sensor may be faulty.
Frequently Asked Questions
Can I drive with the TPMS light on?
You can drive short distances, but you should check and inflate your tires as soon as possible. Underinflated tires wear faster, reduce fuel economy, and generate excess heat that can lead to blowouts. If the light came on suddenly while driving, pull over safely and inspect the tires visually for punctures or damage before continuing.
Why does my TPMS light come on only in winter?
Cold air contracts, lowering tire pressure by about 1 PSI for every 10-degree drop in temperature. When winter arrives, check your tire pressure and inflate to the recommended level. The light should turn off once pressure is correct. This is normal seasonal behavior, not a sensor failure.
What is the difference between the pressure on the tire and the pressure on the door jamb?
The pressure on the tire sidewall is the maximum pressure that tire can safely hold. The pressure on the door jamb is the correct operating pressure for your vehicle. Always inflate to the door jamb pressure, not the sidewall pressure, to may support proper handling, fuel economy, and tire wear.
Do I need to replace all four TPMS sensors if one fails?
No. You only need to replace the sensor that has failed. However, if your vehicle is older and multiple sensors are failing around the same time, replacing all four at once may be cost-effective since labor is similar and sensors are inexpensive relative to the service call.
Can a slow leak trigger the TPMS light?
Yes, if the leak causes pressure to drop 25% or more below the recommended level. A slow leak that loses 1 PSI per week will eventually trigger the light. Check your tires weekly with a manual gauge to catch slow leaks before the light comes on. A tire shop can locate the leak using soapy water or a submersion test.