How your tire pressure monitoring system (TPMS) keep you safe and informed on the road

If you have a newer vehicle, chances are good it has a tire pressure monitoring system (TPMS). These systems continually check your tires and warn if the air in them falls below the correct pressure.

“Properly inflated tires make a vehicle handle better, and you need to be warned if you have rapid deflation,” says Hugh Charvat, president and CEO of Schrader International, which makes TPMS systems. “It gives you the warning even before you feel it through the steering wheel.”

Almost all TPMS systems used today are direct systems, meaning there’s a pressure sensor inside the tire. Most sensors are part of the valve stem, but a few use a sensor strapped to the wheel inside the tire. A small number of automakers use indirect systems, which use the anti-lock brake sensors to check the speed of each wheel and determine if one is turning more slowly, indicating a low tire.

The systems are set to the proper pressure for the car, and warn if a tire drops 25 per cent or more below it.

If your tire warning comes on when it’s really cold, but goes off after you’ve been driving for a while, it could be that one of your tires is very close to the warning threshold.

“Temperature has an impact on pressure, because gas expands and contracts,” Charvat says. “The TPMS (warning) will come on, but when the tires warm up, the light will go off because the pressure inside the tire will increase. It’s telling you to check the tires.”

This could be because you have a leak in one tire, or that you haven’t checked your tire pressure in a while. Tires are permeable, meaning that air molecules will gradually pass through them, and it could be that you’ve finally lost enough to set off the warning.

If you change to winter tires each season, but don’t have pressure sensors in your winter wheels, your TPMS system won’t work. “It’s a smart investment to buy four additional sensors to maintain the integrity of the system and keep it functioning,” Charvat says. “If you have a slow or rapid leak, you’re putting yourself at risk because you’ve intentionally disabled a safety system.”

The sensors contain batteries, and after about 10 years, they’ll probably need replacing. A blinking TPMS warning light could indicate either a dead sensor battery or a malfunctioning sensor, and should be checked as soon as possible.

And even though you have a warning system, you should still check your tire pressure each month. A tire could be low enough that it’s affecting your fuel economy, even though it’s not down to the warning stage.

  • Mandatory. Tire pressure monitoring systems are mandatory on all new cars sold in the United States. They’re not required in Canada, but most new cars have them.

  • Signs. Depending on the vehicle, you may have a warning light that indicates one of the tires is low, or a display that shows the specific tire pressure.

  • Advice. The proper air pressure for your tires is on a sticker inside your driver’s door jamb, the glovebox door, or the fuel filler door.

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