What You Should Do When A Tire-Pressure Light Flashes

Tire-pressure warning lights are typically located in the gauge cluster of an automobile's dashboard. Warning lights are usually yellow or amber and resemble a cross section of a tire with an exclamation point and/or the letters "TPMS." (You can see one in the photo above, just to the left of the speedometer.) This small telltale illuminates to inform you of low air pressure in one or more tires when that issue is detected by the vehicle's tire-pressure monitoring system (TPMS).

In general, the light will come on when the air pressure in one or more tires is outside the recommended range. Since the tires' optimal performance and safety benefits are realized within a specific range of air pressure, measured in pounds per square inch (psi), the warning light may illuminate when pressure has dropped as little as 10 percent below the recommendation—long before low pressure is visible to the eye.

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Some of the more sophisticated tire-pressure monitoring systems will tell drivers which tire is out of range or display real-time air pressure in each tire—including spare tires, in some cases.

If your tire-pressure warning light comes on, don't ignore it; you could be getting a flat.

Low pressure could result from a leak or simply from the tendency of a tire to lose about a pound of air pressure every month, as well as a pound for every 10-degree drop in temperature. So if your tires are inflated properly in the summer, they could be low enough by the winter months to prompt the tire-pressure warning. Similarly, if a tire-pressure light illuminates on a cool morning, it could shut off if the ambient temperature climbs high enough to bring the tires back to an acceptable pressure. Tires warm up as you drive, raising their internal pressure by about 3 psi, which is another reason the TPMS warning might be on first thing in the morning and off later in the day.

Either way, whenever a tire-pressure warning light turns on, it's time to check your tires with a tire-pressure gauge, which costs as little as $5. A monthly pressure check of all your tires can help you keep them at the optimal level of inflation and will enable you to identify slow leaks early—possibly even before the pressure drops low enough for the warning light to come on.

If your TPMS warning light does come on, find the closest gas or service station and check the pressure of all four tires (plus the spare, if applicable), adding air to any that fall below the range listed on a sticker inside the driver's door. Once the tires are properly inflated, the light may go off after you've driven a few miles. If the light doesn't automatically turn off after about 10 miles, the TPMS may need to be reset, as directed in the vehicle's owner's manual. If the light comes on and all your tires are within the acceptable range, there's a chance that you have a malfunctioning tire-pressure monitoring sensor that needs to be replaced. No matter what the issue turns out to be, pay attention if the tire-pressure light turns on; you'll be safer for it, and you might also avoid damaging your tires.

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Steve SilerSteve Siler started a car column at his college newspaper in 1995 and has been writing about cars ever since, with his musings and photographs having appeared in scores of different print and online publications. Born in Los Angeles, California, where he still lives and works when he's not on a media drive program or covering a car show, Siler brings a West Coast perspective to his coverage and has been a contributor to Car and Driver since 2006.