We’ve got the answers—Mondays when the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re taking a closer look at tire pressure monitoring systems (TPMS).

Q: Can you provide some basics regarding the TPMS on my truck?

A: Tire pressure monitoring systems were first adopted by the European market on a few luxury and high performance vehicles in the 1980s. Domestically, the TREAD Act legislation mandates the use of appropriate TPMS technology on all light vehicles (less than 10,000 pounds) sold after September 2007 in order to alert drivers of severe under-inflation. Accordingly, all 2008-up passenger cars sold in the United States are now TPMS equipped; in Europe all of the 2012 and newer model year passenger cars are TPMS equipped. Exceptions do exist, such as certain specified commercial vehicles, pickup trucks with dually rear axles, and vehicles over 10,000 pounds GVWR.

There are two types of tire pressure monitoring systems: indirect and direct. Indirect TPMS methods often employ portions of the vehicle’s ABS, ESC and/or TCS. Detection is often based on roll radius, resistance, or scrubor some variation of each. Input is achieved through the slightest measurable fluctuation picked up by wheel speed sensors to determine tire inflation condition. Some of the more advanced indirect methods use a form of spectrum analysis to monitor frequencies specifically produced by under-inflated tires, since frequencies and oscillations of the tire and wheel assembly are extremely sensitive to inflation pressure. Indirect TPMS drawbacks do exist. They are not capable of delivering exact pressure or temperature values and will require a manual reset once tire pressure has been correctly adjusted. Indirect systems are also highly sensitive to certain road surfaces and conditions, driving speed and driving style, and the possible influence of changing tire style.

Direct TPMS is currently the most popular system and is based upon the use of an internal or external pressure sensor located in or on each tire. Here, sensors are used to measure the actual pressure within the tire and wheel assembly which is then transmitted to a receiver often in a display in the instrument cluster or in-dash monitor. These systems report direct tire pressure values with many systems also reporting inside tire temperature. The systems may vary by transmitting method, but all are now capable of identifying under-inflation locations. Drawbacks to this design are associated with the harsh environment found in or near the tires themselves and the limited life of the self-contained battery. Extreme temperature fluctuations, moisture, vibration, and physical forces are constantly working against the sensor and the battery.

Different system configurations and programming have been used to try and extend the service life of the sensor and the battery. Previous and current editions of OE direct TPMS do not incorporate a replaceable battery. With factory designs offering a five to ten year service life there is ultimately a 100-percent failure rate. Aftermarket companies, including Dorman, Standard Motor Products, and Stack Gauges, have embraced the opportunity to work within the TPMS replacement arena. All you need to do is use your favorite web search and look for TPMS. There you’ll see the numerous possibilities for additional information and understanding along with the manufacturers’ offerings for replacement TPMS sensors and hardware.