A tire pressure warning light, like the one below, is a computerized measurement that alerts you when the pressure of one or more of your tires fall below 25% of the manufacturer's recommended psi.
Some cars alert you if your tire's pressure is too high, but the majority of vehicles focus on the more common problem: under-inflation.
If your light comes on
Visually inspect all four tires for damage, then use a tire pressure gauge on the tire (or tires) that your system indicated had low pressure.
Compare the tire's psi with the manufacturer's recommended psi, which can be found in your owner's manual or on the sticker inside of your driver's side door jam. (To find this sticker, click here .)
If pressure is low, add air until it reaches the proper pressure. If your light continues to stay on, take your vehicle to an authorized tire dealer immediately.
Source: Robertson Tire and Michelin