TPMS is an automated system that monitors the air pressure in a vehicle's tires. When air pressure in one or more tires drops 25 percent or more below the correct pressure, a warning indicator alerts the driver. TPMS typically delivers these alerts to the driver through one of two types of warning lights on the dashboard.
1. The first uses the official TPMS symbol, which is a cross-section of a tire with an exclamation mark in the center.
2. The second is a top-view graphic image of a car that indicates which tires are low.
Tire pressure is monitored through one of two methods: direct or indirect. Direct TPMS monitors the actual air pressure inside each tire via a sensor mounted within the tire. Indirect TPMS measures tire pressure by monitoring the speed and rotation of each individual wheel. When a significant variation in speed and rotation is detected in one or more wheels when compared with the others, it is often an indication of underinflation. This information is then transmitted to the vehicle's on-board computer, and the driver is alerted.
However, while TPMS systems offer increased safety to drivers through low pressure warnings, they are not meant to be a substitute for proper tire pressure maintenance. Both the NHTSA and the AAM urge drivers to check their tire pressure at least once a month and always prior to a long trip. In addition to making drivers aware of the new standard for TPMS, the "Check My Tires (link to http://www.checkmytires.org/flash.html)" website also offers a "how to" list for proper tire inflation, explanations of the various reasons why correct tire pressure is important, and links to a number of safety-related resources. Be sure to read our article on the importance of correct air pressure as well for even more in-depth information.
Even though TPMS has only recently become standard for all vehicles, a number of older models already have them installed. Approximately 20 percent of 2006 vehicle models came pre-equipped with TPMS, and that number increased to 70 percent in the 2007 model year. If you are unaware if your vehicle has TPMS installed, check your vehicle owner's manual.
Sources: NHTSA, AAM, Intelligent Tire Conference