This blog post is a collaboration job from Repair Pal

Proper tire pressure is important to the safety and efficiency of your car. And if you own a vehicle made since 2007 or so, you’ve got a leg up on making sure your tires are properly inflated.

The tire pressure monitoring system (TPMS) monitors the air pressure in each of your tires. If one or more of them drops to the point where it’s unsafe to drive on, the TPMS warning light in your instrument panel will come on. The light is usually yellow, and displays an image that looks like a cut-away view of tire with an exclamation point inside it.

By Stephen Fogel

Why tire pressure is important

Having the correct amount of air in your tires provides many benefits:

  • Better support for the weight of your vehicle
  • Easier dissipation of the heat that builds up in your tires
  • Better accelerating, cornering and stopping
  • Helps your tires last as long as possible
  • More cushion against the bumps you drive over

On the other hand, not having enough air in your tires can cause a variety of safety and reliability problems. Driving on underinflated tires creates a serious heat buildup within them. This excessive heat can cause blowouts that result in catastrophic accidents. A spate of these crashes led to TPMS being required on all new cars in the U.S.

How TPMS became mandatory

In 1996, state agencies in Arizona began to report serious problems with the Firestone tires used on their official vehicles. Firestone claimed that the vehicle owners had abused the tires by not keeping them properly inflated.

Over the next few years, more than 200 people would die in incidents related to Firestone tire blowouts and tread separations on Ford Explorer SUVs. The tires failed from intense heat buildup, often due to underinflation.

In response, Congress passed the TREAD Act in 2000. This legislation mandated that, starting in September 2007, every passenger vehicle sold in the U.S. be equipped with a TPMS.

Similar systems had been installed on certain cars since the 1980s — primarily European luxury and performance models — but had not yet become commonplace in the U.S. before the TREAD Act.

How the TPMS works

Whenever you turn the key, all your car’s warning lights — including the TPMS one — will briefly light up as your vehicle checks its systems. They should go out once the engine has been running for a few seconds.

Your TPMS can be one of two different types of systems: direct or indirect. The difference is in the way the system determines whether your tires are properly inflated.

Direct system: Most cars use this type of TPMS. Direct systems use a pressure sensor and a transmitter inside each tire or wheel assembly. These sensors are usually attached to the valve stem, although some vehicles may have them mounted on the wheels.

Direct systems monitor the pressure within each tire and send a low-pressure signal to a receiver inside the vehicle whenever a tire drops 25% below its recommended pressure. This turns on the warning light on the dashboard and triggers an audible warning. Some systems will tell you which tire is low, and some will even give you the exact pressure in each tire.

Indirect system: This system uses the wheel speed sensors that are part of your anti-lock braking system. Your car’s computer constantly analyzes this data, and can instantly identify the changes in tire size that are caused by a loss of tire pressure. If the computer notices a significant change that translates to a pressure loss of 25% or more, it will trigger the warning light and sound.

What to do when the warning light comes on

If your TPMS warning light comes on, it requires immediate attention. One or more of your tires has dangerously low pressure. Here are a few scenarios:

The light comes on when you start your car

If you start your vehicle and the TPMS light stays on, don’t drive it. Shut the vehicle off. If you have a system that tells you which tire is affected, get your tire gauge out of the glove box and check that tire’s pressure.

If you don’t know which tire it is, you’ll have to check them all. In fact, it’s always a good idea to check them all — there may be another low tire that’s close to setting off the light. Verify the correct tire pressures by checking the sticker located in the driver’s door jamb, or reviewing the owner’s manual.

If you have an air compressor on hand, use it to pump the tire up to the recommended pressure. If you don’t have one, and the tire is holding around 75% of the recommended pressure, drive slowly to the nearest gas station and fill the tire using the station’s air hose. Make sure that all of your tires are correctly inflated.

Listen for a hissing sound that may indicate a puncture, which may be repairable by your mechanic or a tire shop. If the tire is flat and won’t inflate, you’ll need to change the tire if you have a spare, use a can of fix-a-flat if you have one, or call roadside assistance.

The light comes on while you are driving

If you’re driving and the TPMS light comes on, hold the steering wheel firmly, slowly decelerate by lifting off the gas, and find a safe place to pull off the road or highway. Don’t make any sudden moves with the steering wheel, gas or brakes. Grab your tire gauge and follow the directions above. The air loss that triggered the light may indicate a damaged tire.

The light comes on and flashes

This can indicate a TPMS malfunction. Pull off the road in a safe place and consult the TPMS section in your owner’s manual for more details. Get out your tire gauge and check your tire pressures, just to be sure that your tires are OK to drive on. If they are, it should be safe to continue, but call your mechanic to get the system checked. If your tires are low, follow the directions above.

The light stays on for several minutes but then goes off

Another factor that can cause your TPMS light to come on is the onset of cold weather. As the temperature drops, so will your tire pressure, especially after the car has been resting for a while. While driving can warm up your tires to the point the light turns off, this is not a safe situation. You’ll want to measure your tire pressure when the car is cold and inflate as necessary before hitting the road.

False alarms: The light comes on, but your tires are OK

The TPMS warning light can sometimes be triggered when there is no problem with your tire pressures. This may be caused by a faulty sensor, located either inside a tire or in the anti-lock braking system. Your mechanic will need to take a look.

About run-flat tires

Run-flat tires are tires that you can drive on for a limited distance after they lose their air pressure. They’re made with very rigid sidewalls that support the tire when it has no air in it. Because of this, it’s difficult to visually tell if a run-flat tire has a low tire pressure. Cars with run-flats will often have sensors that let you know the tire has lost its air and is technically “flat.” Check your owner’s manual for additional information on how your car’s system works.

Tips for TPMS and good tire care

  • Have a tire gauge and a portable compressor in your car.
  • Check your tires at least monthly and maintain the correct pressures.
  • Always check tires when they are cold, before driving on them, for the most accurate readings.
  • The TPMS will only alert you when your tires are dangerously low. Do not use it as a reminder to check your tire pressures.
  • Consult your owner’s manual for the details and instructions for your specific TPMS, and know how it works.
  • Always tell your mechanic or tire technician that you have TPMS before they work on your tires.
  • You can usually reuse your in-tire sensors when you get new tires, but keep in mind that their battery life is around 10 years. At that point, they will need replacing.