Trouble with Tire Pressure Monitoring Systems

Types of TPMS
There are two types of TPMS: Indirect and direct. Indirect systems don’t measure tire pressure but rather uses the anti-lock braking system sensor to calculate how far one tire rolls in comparison to the others. Direct systems have sensors on the wheel that relay actual pressure to the car’s computer. Indirect TPMS have a large margin of error, while top-quality direct systems can be very precise. It’s unknown if any vehicle manufacturers set their direct systems to trigger significantly higher than the required threshold. At least one major manufacturer that uses direct TPMS still employs the 25 percent threshold.


Those who live in cold areas and have the luxury of a heated garage are often befuddled by TPMS. They responsibly set their tire pressure to the vehicle manufacturer-recommended pressure inside a 65-degree garage before driving onto frigid roads. Within a few miles, the TPMS illuminates. False warning? No, the extreme cold has reduced the tire pressure. Tire pressure changes about one psi with every 10-degree Fahrenheit change in outside temperature. Tires set to 32 psi inside a 65-degree garage will drop to about 27 psi if it’s 10 degrees outside. Likewise, those who set tire pressure on a hot autumn day that’s followed by a cold snap will get a TPMS warning. The tire requires its pressure to be correct for the outside temperature.


Other things that cause TPMS issues include the fact that it’s not unusual for a tire to lose almost one psi a month. Also, tire gauges aren’t always accurate. We once purchased the most expensive tire gauge in the auto parts store and it read two psi optimistic: The tires were really at 30 psi when the gauge said 32 psi. Another thing that causes TPMS irritation is the calibration process, which differs among systems and manufacturers and can cause false warnings if performed incorrectly.


One thing TPMS does well is alert the driver of an actively leaking tire. If the TPMS illuminates, believe it: Slow down smoothly, find a safe place to stop and check your pressures. The bottom line: It’s still up to you to check and set your tires pressures once a month. Don’t rely on the TPMS, but don’t ignore it either.

About the Author
Mac Demere is a vehicle and tire test driver, high-performance driving instructor, precision driver for TV and film, and a former racer who competed in the NASCAR Southwest Tour and 24 Hours of Daytona.