Understanding your Tire Pressure Monitoring System

If you own a newer vehicle, you are likely familiar with the horseshoe-like symbol and exclamation mark that illuminates on your dashboard.  This is your tire pressure monitoring system, or TPMS, warning you that one or more of your vehicle’s tires are under-inflated and may pose a safety hazard.

A Brief History

This indicator light did not always exist. Checking your tire pressure once required you to manually check each tire with a tire pressure gauge tool. However, after the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) act was passed, legislation required most vehicles sold in the United States after 2007 to include a TPMS. There are two types of tire pressure monitoring systems: Direct and Indirect.

Direct TPMS

A direct TPMS monitors tire pressure level and sometimes temperature, using sensors in each tire. All of this data is then sent to a central control module to be analyzed and if it determines your tire pressure to be low, the indicator light illuminates. Each sensor has its own unique serial number so the system can distinguish between each individual tire. Some advantages of a direct TPMS are the more accurate tire pressure readings, long lasting battery life and freedom from having to reset the system each time you have your tires rotated or serviced.

Indirect TPMS

An indirect TPMS measures the rate of revolution for each wheel through the anti-lock brake system. This information is then passed to the vehicle’s computer and compared with speed and other operation data. If a wheel is spinning faster than normal, the computer determines that it is underinflated and illuminates the dashboard alert. While the indirect system is less expensive and requires less maintenance than the direct system, it is also less accurate. If you purchase a different size tire or experience uneven wear, you will likely get an incorrect tire pressure reading. Additionally, you must always make sure to reset the system after servicing your tires.

My Tire Pressure Light is On. What now?

Your tire pressure light just lit up on your dashboard, alerting you to an underinflated tire. So, what now? First, use a tire pressure gauge to manually check pressure and inflate accordingly. The manufacture’s recommended PSI is typically between 30-35, however, you can find this information on a sticker in your door jam, trunk lid, console, fuel door or in your owner’s manual.

If the TPMS light goes on and off, it could be due to the temperature causing pressure fluctuation. This can sometimes happen when the temperature drops over night and correct itself during the day, as the temperature rises, or heat is generated from driving. If the warning light flashes and stays on, there may be a functionality issue with your tire pressure monitoring system, and you should have an experienced technician conduct an inspection.

If your tires have been serviced and your tire pressure light continues to illuminate, there may be a few different factors causing a slow leak. Have your tires checked for a puncture or tear, deteriorating valve stems, mounting issues causing air to leak at the rim or the rim itself.

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