A tire pressure monitoring system is not a substitute for checking the pressure of your tires each month. While tire pressure monitoring systems do serve a purpose, they do not (and never were) intended to replace the need for regular tire maintenance. These systems are, at best, an emergency warning system and the technology behind these systems is far from being perfect.
After a number of Firestone tires failed, resulting in the recall of 6.5 million tires, President Bill Clinton helped push through the TREAD Act, which is a comprehensive law intended to provide enhanced safety protections for tire consumers. Although the tire industry successfully fought off many of the proposed protections, one that remained is a requirement that tires have tire pressure monitoring systems (also known as TPM systems or TPMS) installed. If your vehicle was produced after September of 2007, it will have a TPM or TPMS system installed. While these systems are a tremendous step in the right direction, tire pressure monitoring systems are not without their faults or limitations.
The TREAD Act established a new Federal Motor Vehicle Safety Standard (FMVSS). This law (FMVSS 138) requires the installation of tire pressure monitoring systems that will warn you when your tire becomes significantly under-inflated. The key word here is “significantly.” For the system to indicate a problem exists, the tire pressure must fall below 25 percent of the manufacturer’s recommended psi. However, it takes less than a 25 percent loss in tire pressure for the tire pressure of a vehicle to begin affecting safety, fuel efficiency, and premature tire wear.
To make matters worse, TPM systems vary greatly from one manufacturer to the next. The best systems out there will provide a constant indication of the current pressure of each tire on the vehicle. Other systems simply emit a warning when the tire has reached the 25% threshold. Monitoring methods also vary and are dependent upon whether the TPMS uses indirect or direct technology.
Finally, many tire service centers have made vocal complaints about malfunctioning, defective, and otherwise faulty tire pressure valve sensors that fall apart inside the tire and present a major safety concern.
Tire pressure monitoring systems vary based on whether the manufacturer uses indirect technology or direct technology. When a TPMS uses direct technology, the system uses sensors located in the tires. When a TPMS uses indirect technology, the system uses the wheel speed and other vehicle sensors to detect tire pressure loss. Whether using direct or indirect technology, the sensors that are used will collect information and transmit the data to an on-board processor. This processor then interprets the sensor signals and warns the driver when the pressure of the tire is below the acceptable level. The warning is given via a gauge, diagram, or simple warning light on the vehicle’s instrument panel.
Generally speaking, direct systems detect a dangerous condition faster and require substantially less maintenance than indirect systems—however, direct systems are more expensive. Indirect systems also suffer from inherent design defects due to the requirement that the vehicle owner recalibrate the system periodically.
As stated above, TPM systems were never intended to replace regular tire maintenance and the technology is nowhere near perfect. It is still important to visually inspect your tires and check your tire pressure each month to ensure safe driving, maximized fuel efficiency, and decreased wear on your tires. While a TPM system is a great emergency warning tool, these systems are not without their limitations. As such, you should not let the safety of your family ride on such a system.
 FMVSS 138 applies to all passenger vehicles with a gross vehicle weight rating (GVWR) of 4,536 kg (10,000 lbs.) or less, except those vehicles with dual wheels on an axle. See http://www.nhtsa.gov/cars/rules/rulings/index_treadact.html
 Reader Comments: TPMS Sensor Corrosion a Big Issue, Tire Review November 8, 2012; Weigh In: Is OE TPMS Sensor Failure a Hidden Problem?, Tire Review, October 26, 2012.