Is this light on in the dash of your vehicle? It's telling you to check your tires air pressure.
There are a few reasons why your tire pressure could be off and some are just due to temperature change. Other reasons could be due to possibly running over a nail or screw or anything sharp that might have punctured a tire. If one tire is way lower that the others, you may need to check and see if there is a nail or something visible and if so, you will need to get this fixed by either having to get a new tire or a simple fix but just plugging it.
1. First check and see if your dash may tell you which tire is low. Some vehicles have this built in. If your vehicle doesn't, get your tire gauge and manually check each tire. If one tire is way lower that the others, this may be because you did puncture that tire.
2. Open your door on your vehicle and look for a sticker that will tell you the required pressure for your tires.
It will look something like the middle sticker in this image. It's a small chart telling you the PSI required in each tire. See which tires are off of the required PSI shown on this sticker. That will be the reason the light is on.
3. Gas stations usually have air pumps for airing up tires. Or use your own compressor at home. Fill the tires up to the recommended PSI by the chart (most vehicles will let you be a few PSI high or low and it will cut the light off). If the tires now have the recommended PSI, the light will usually go off.
Note: each manufacturer is different and some tire pressure monitor systems need to be reset. Check your owner's manual if you have the right PSI and the tire light is still on. You may be able to manually reset your tire pressure monitor light. You could also have a faulty tire pressure monitor in the tire and it may need to be replaced. If you have the right PSI and you checked the owner's manual and still cannot get the light to go off, you may need to get the tire pressure monitor replaced in the tire. In that case, you will need your monitor checked at a service center.