How Does a Tire Pressure Monitoring System Work?

From punctures to improper wheel alignments, there’s a lot that can affect or damage your tires’ ability to maintain pressure. Luckily many modern cars come with sensors to let you know in real-time if there’s a problem. But these tire pressure monitoring systems aren’t infallible, which is why some OEMs are working on updating them.

How does TPMS work?

Your car’s TPMS, as with many of its other safety and driver-assistance features, relies on specialized sensors, Car and Driver reports. Many are mounted in the wheel, TirePlus reports or built into the tire’s valve stem. Most aftermarket systems, The Drive reports, are of one of these so-called ‘direct’ monitoring designs.

As the name implies, direct tire pressure sensors explicitly measure air pressure. These battery-powered sensors send radio signals to a receiver within the car. When the pressure gets too high or low, the TPMS warning light comes on.

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Some cars, though, have tire pressure sensors linked into the ABS system. These ‘indirect’ sensors, Bridgestone explains, don’t actually measure pressure, though. Instead, they measure tire rotation. An improperly-inflated tire doesn’t roll at the same speed as a properly-inflated one. So, if the TPMS notices a speed imbalance, it triggers a warning light.

A blue 2021 BMW M2 CS taking a tight track corner
2021 BMW M2 CS

Recently, though, some suppliers have been trying to improve upon TPMS design. BMW and Michelin, for example, have collaborated on a ‘connected tire’ which uses sensors to measure not just pressure, but tire temperature, too. The goal is to use this data to provide the driver with valuable training feedback.

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 In addition, The Drive reports Bridgestone and Microsoft are working on a system that can monitor tire damage as well as pressure. This new system would also detect if the tire hits a pothole or other irregularity, and tag it via GPS. Then, using vehicle-to-vehicle communication, it would let other cars know to avoid that spot.

As of this writing, Microsoft’s ‘TDMS’ is available in new VW, Nissan, Mitsubishi, and Renault vehicles. It’s unknown when, or if, the technology will spread to other brands. However, it could help prevent some of the problems which can plague conventional tire pressure sensors.

Can it fail or break?

While TPMS is a helpful tool, it’s not infallible. Firstly, the warning light typically only illuminates when the tire pressure is at least 25% too low, Edmunds reports. Secondly, as with engine mounts, catalytic converters, or any other sensor, the ones in your tires can and do break.

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Because direct sensors are part of your wheel or tire, they’re subject to road imperfections. This means a severe-enough impact, such as with a deep pothole, can damage them. As can road debris or severe weather, reports. Usually, that’s signaled by the TPMS light flashing, rather than staying lit.

In addition, tire pressure sensors operate using radio frequencies. If the signal gets blocked or encounters interference, you can experience a false malfunction light. This can happen, for instance, if you fit a snow tire that isn’t compatible with your TPMS.

Direct sensors, though, have one more potential failure point. Unlike indirect ones, which are wired into the car’s electronics, direct tire pressure sensors have their own batteries. Over time, these go flat, and the whole sensor needs to be replaced. And, as with replacing sensors for adaptive cruise control or automatic emergency braking, this requires a system recalibration.

For all these reasons, while TPMS is a helpful tool, it shouldn’t replace a regular tire inspection.

Why is proper tire pressure important?

A mechanic measures a tire's pressure using a handheld gauge
OMSK, RUSSIA – OCTOBER 27, 2018: Checking tire pressure on a car fitted with winter tires | Dmitry Feoktistov/TASS via Getty Images

Maintaining proper tire pressure may not seem as vital as, say, making sure your engine has enough oil. However, it is still an important maintenance task. That’s why OEMs put the recommended tire pressure on a sticker in the door jamb.

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If a tire is under- or over-inflated, Car and Driver explains, it messes with the contact patch. This means your car doesn’t handle as well or as safely. That’s why Chevrolet attempted to use tire pressure to correct the rear-engine Corvair’s flaws. An incorrectly-inflated tire also doesn’t absorb shock as well, which could result in further suspension or TPMS damage.

Plus, a tire without enough pressure flexes more, AAA explains, which causes excessive heat and accelerated wear. Under-inflation also increases rolling resistance, which makes you burn more fuel.

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