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The Dual Ways Your Car Checks Your Tire Pressure

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Tire pressure warning light

For many people, the Tire Pressure Monitoring System on their vehicle is just a light on the dashboard. However, after a moments’ reflection, I realized I have no clue how it works. It turns out, there isn’t a single way your car tells how much tire pressure you have—there are two.

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Direct monitoring

First, there is the direct tire pressure monitoring system. This is the more straightforward method—in it, each tire contains an individual sensor, which measures pressure and sometimes temperature. In this case, the sensor uses radio signals to communicate with the vehicle’s central computer, which alerts you to any problems.

There are some problems with this kind of sensor, though. Since it’s wireless, the sensor operates on batteries, but the battery runs out eventually at about the decade mark. Usually, you can’t just replace the battery, so you have to replace the entire sensor. Also, the sensor stem is vulnerable to snapping if you accidentally hit a curb or are involved in a crash. Finally, the mechanic often has to program a new sensor into the control module, and the wireless system can just fail over time.

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Indirect monitoring

The second method is indirect tire pressure monitoring. There sensors, rather than trying to measure tire pressure directly through a probe in the tire, get a little sneaky. They use wheel speed sensor data to interpret the size of your tire based on how fast it rotates. An under-inflated tire is smaller than a fully-inflated one, so the system watches until it’s a given amount “smaller” than the others, and then alerts the driver.

This skirts many of the problems of direct pressure monitoring systems, but has its own problem in that you need to reset it whenever the tires are inflated. Otherwise, it will assume that the tires are way too full and set off warning bells.

News Source: Tires Plus, How Stuff Works