Why is my tire pressure light on but my tires look fine?

Concerns & risks

You were trying to get to work on time, but the moment you started the car a little orange horseshoe with an exclamation point lit up on the dash. You walked around the car, kicked a tire, and everything looked normal.

Driving on a low tire hurts handling, braking and tire life.

Causes & evidence

Underinflated tires are hard to spot by sight, and the light only comes on when a tire is significantly low. Cold mornings can trigger it too. See tire pressure and tread.

What to do

1. Check all four tires (and the spare) with a gauge.
2. Fill to the pressure on the driver's door jamb label, not the tire sidewall.
3. Recheck after a few days; a tire that keeps dropping may have a leak.

Common mistakes: Common mistakes: judging pressure by looking. A tire can be well under the recommended pressure and still look fine, especially radials. Another mistake is checking right after driving, when warm tires read higher; check cold, before you drive or after the car has sat a few hours. Gas station gauges can be worn, so your own gauge is more reliable. If the light comes on and the car pulls, vibrates or a tire looks obviously low, slow down and pull over somewhere safe. Some cars need a TPMS reset after filling; your owner's manual explains how. If the light flashes and then stays on, the sensor system itself may need service.

Speed Man tip: Keep a cheap pressure gauge in the glovebox.

Wrap-up: Low tires are hard to see. Use the door-jamb number. Repeated drops mean a leak.