You've likely heard of TPMS in recent years, perhaps because of legislation requiring the use of such systems. Maybe you heard when purchasing a new car in the last few years that your vehicle would have TPMS. Either way you heard about it, you may not know exactly how it works, and why the government even mandated the use of such systems, so today we'll focus on uncovering details of TPMS.

After Firestone recalled over six million tires over tread seperation (likely caused by improper inflation) in 2000, lawmakers began to discuss why better systems were not available to monitor the tires condition. In 2005, final rules were established that would soon require all new vehicles to have a Tire Pressure Monitoring System. Since legislation in 2005, the phase in of TPMS was slow- 20% of 2006 vehicles had TPMS, 70% of 2007 vehicles had TPMS, and finally 100% of 2008 and newer vehicles have or will have TPMS.

How's it work? There are a few different systems, but I've cover the most popular. Sensors are mounted on the rim of your tire, under the rubber. On some systems, these wireless (radio frequency) sensors take readings and send them to the vehicle's electronic control unit, or ECU. The ECU then compares the numbers and sends an alert to your dashboard if it senses one of those numbers too low.

The sensors in your tire may be battery powered. There is a brand new system that does not require batteries that may make its way to new vehicles in a few years, but for now, many of us with newer vehicles have sensors containing batteries. These batteries typically will last anywhere from seven to ten years.

Some TPMS systems also incorporate vibration sensors and other items to determine if a tire is flat or low on pressure. Basically, all these systems are designed to alert the driver if one or several tires are lower on pressure then they should, or if they are lower on pressure than other tires.

For vehicles that don't have TPMS installed, there are standalone systems, but beware- they don't come cheap. Having said that, replacing sensors on a vehicle already equipped with TPMS can be expensive as well. You can expect to pay $35-$50 when getting new tires to "rebuild" your TPMS sensors (replacing valve stem, etc.), or paying $50-$200 to replace a single TPMS sensor, depending widely on system, manufacturer, etc.

If you want to get another set of wheels (for winter), be prepared to install TPMS sensors on your new wheels as well, or risk having the TPMS alert light permanently lit. There are ways around it, but when dealing with your own safety and safety of your passengers, it is the best choice to make sure the TPMS system runs as designed.

Be safe out there, and watch for your TPMS alert. Should it ever turn on, I would suggest immediately stopping and checking your tires for pressure!