Tire pressure light on? What it means and what to do

The tire pressure light is the yellow symbol that looks like a horseshoe with an exclamation point in it. It means at least one tire has lost a lot of air, and it almost always comes on at a bad time: early, cold, and on the way somewhere.

Usually the fix is a few minutes at an air machine. Sometimes it's a nail, and the pattern of the light tells you which.

What the light means

Every car sold in the US since the 2008 model year has a tire pressure monitoring system (TPMS). Under the federal standard, FMVSS 138, the light has to come on when a tire is 25% or more below the pressure on your door sticker. For a car that calls for 35 PSI, that's around 26 PSI.

That's a big drop. You won't always see it by looking at the tire, but you'll feel it in the steering, the braking and your fuel economy, and an underinflated tire runs hotter on the highway.

Solid light

One or more tires is low. Check all four and fill them.

Flashing light, then solid

On most cars, a light that blinks for about a minute after you start the car and then stays on means the monitoring system itself has a problem. The usual culprit is a sensor battery; they're sealed inside the sensors and tend to give out after several years. Your tires might be fine, so check them with a gauge anyway. A tire shop can test and replace the sensors.

Why it comes on when it gets cold

Air pressure drops about 1 PSI for every 10°F the temperature falls. Set your tires to 35 PSI on an 80°F afternoon and they'll read around 31 on a 40°F morning, before you've done anything wrong. If a tire was already a little low, the first cold snap of fall pushes it past the warning line.

This is why the light often goes off by the afternoon. The tires warm up, the pressure climbs back over the threshold, and the light clears. The tire is still low, and the next cold morning the light will be back.

What to do, in order

1. Look at all four tires. If one is visibly flat, or the car pulls hard to one side, pull over somewhere safe and put on the spare or call for help. Driving on a flat ruins the tire and can damage the wheel.
2. If they all look normal, drive gently to the nearest air. Our map of free air for tires near you shows the closest free spots with driving times, and the Open now filter hides places that are closed.
3. Check every tire with a gauge, including the ones that look fine. The light doesn't say which tire is low on many cars.
4. Fill all four to the pressure on the sticker inside the driver's door. Our step-by-step guide to putting air in your tires covers the air machine.
5. Drive for a few minutes. The light should go out. If it doesn't, check the owner's manual for a reset button or menu setting.

If the light keeps coming back

Once after a cold snap is normal. Again within a few days means a tire is leaking. Check which one is low each time; it's usually the same tire.

The common causes are a nail or screw in the tread, a leaky valve stem, or a bad seal where the tire meets the wheel. A tire shop can find and patch most of these in under half an hour. Discount Tire repairs flats for free when the tire can be safely fixed, and Les Schwab repairs them free on tires bought there. Both will top off your air for free.

If the tire is fine but the light still won't stay off, suspect the sensor. That costs money to fix, and how much depends on the car, so it's worth asking for a quote before you agree to new sensors on all four wheels.

Checking before the light comes on

The light is a last warning. A tire can be 20% low, wearing unevenly and costing you gas, without ever triggering it. Checking once a month and before long trips catches that. The tire pressure guide has typical pressures for cars, SUVs, trucks and spare tires.

Low on air right now? See the closest free air, open now, with driving times. Find free air near me →

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