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It can be tough to tell if the air in a tire is too low or too high just by looking at it. Luckily for us, most newer cars have a Tire Pressure Monitoring System (TPMS) that continuously monitors the pressure in your tires through sensors located in the tires(direct system) or the use of wheel speed and other vehicle sensors (indirect system). The information collected by the sensors is transmitted to an on-board processor that interprets the sensor signals and warns the driver when tire pressure is below the minimum acceptable level by illuminating a warning lamp.

Tire Pressure Monitoring Sensors

Most vehicles use a direct system, in which a tire pressure sensor is in each tire. That sensor is linked to your vehicle’s onboard computer to directly measure air pressure.

A small number of vehicles use an indirect tire pressure monitoring system, which monitors the relative speed and rotation of the vehicle’s wheels and alerts you if one wheel is significantly out of sync with the others.

Underinflated tires can take a toll on your wallet and your safety by affecting your gas mileage and shortening tire life due to uneven wear. Even more importantly, underinflation can stress a tire to the point of failure, putting you in jeopardy of having a blowout on the road.

Tire Pressure

There are many things that can come into play and affect tire pressure, including temperature changes, tire punctures, or other damage. Tire pressure can drop about 1 psi (pounds per square inch) for every 10 degrees and tires lose about 1.5 psi per month as air escapes from the tire naturally.

On cold mornings, the TPMS light lamp may light up for a brief period and then turn off. This usually is caused by slightly low tire pressure that falls below the warning threshold overnight, but returns to an acceptable level as the tires heat up. In the summer, tires can overinflate, also triggering your TPMS light. If you notice this happening, bring your car into Pep Boys for a free tire pressure check.

TPMS is required by The National Highway Traffic Safety Administration on all vehicles produced after September 2007. Some earlier models may also come equipped with TPMS. Check your owner’s manual to be sure. According to the National Highway Traffic Safety Administration, TPMS is estimated to reduce the number of annual motor vehicle crash fatalities by about 120 and the annual number of injuries due to motor vehicle crashes by about 8,500, when all passenger vehicles are equipped with TPMS.

Remember, TPMS is not a cure-all or a replacement for proper air pressure maintenance—it’s important to check your air pressure regularly. Vehicle aging and other factors can impact the system readings. Your car will handle better, save you gas, and you’ll be safer on the road.

Nonetheless, if your TPMS light comes on, you should check your tire pressure. You can locate your recommended tire pressure in your owner’s manual or in the doorjamb of your driver’s side door. Or, if you’d like one of our ASE-certified technicians to take a look, schedule a free tire pressure check at your nearest Pep Boys.