Aaron Widmar
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TPMS Explained: How Does the Tire Pressure Monitoring System Work?

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low tire pressure indicator icon owners manual
Photo: The News Wheel

An under-inflated tire is dangerous. It affects the wear and handling of your car and is more likely to tear the rubber. Unfortunately, you might not even realize that tire pressure is low until it’s too late.

As a safety precaution, your car has a Tire Pressure Monitoring System that will warn you when a tire’s air pressure is dangerously low. Here’s how that technology works and how it became an essential component.

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How the Tire Pressure Monitoring System measures the air in your car’s tires

Tire Pressure Monitoring Systems have been a standard feature on all U.S. vehicles since 2007 due to government safety mandates, though the technology has been around in luxury and race cars since the 1980s.

There are two types of TPMS, as Ronald Montoya of Edmunds explains: direct and indirect.

An indirect system, or iTPMS, monitors the size and rotation speed of a wheel to determine if it’s low, because an under-inflated tire has a different diameter and rotation rate than a fully inflated tire. They’re simple, cheap systems, but because they don’t actually measure the air pressure itself, they can often be inaccurate.

Most U.S. vehicles use a direct TPMS system. dTPMS uses an electronic sensor within each tire to monitor the actual PSI and transmit it to the car’s central computer. This allows the dTPMS to identify if a tire is low whether it’s moving or idling.

Newer, high-line dTPMS systems share these real-time PSI readings with the driver, allowing you to see the current pressure levels on the digital information cluster above the steering wheel. If this information isn’t displayed, you have a low-line dTPMS that only uses the readings to warn you when they’re too low.

TPMS light
Photo: Hydrargyrum

Whichever version your car has, the TPMS will illuminate a warning light on the dashboard when it senses a low-pressure tire (the icon being an underinflated tire with an exclamation point inside it). If this happens, that means inflation has fallen to 25 percent or lower than the recommended level, so you need to pull over and get help immediately.

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