Tire pressure monitoring system: what, why, how

2015 Lexus NX 200t
Many new vehicles sold in Canada, including this 2015 Lexus NX 200t, come with a tire pressure monitoring system. Photo by Benjamin Yong.

A tire pressure monitoring system (TPMS) is one of those useful features that might come installed on your vehicle without you even realizing it. Unlike in the United States where it has been mandatory on passenger cars since 2007, Canada has no such requirement, although many new models sold here do include a TPMS. Scroll down to find out more about this innovative safety technology.

TPMS indicator light


TPMS has one simple task: to let the driver know when one or more tires are under-inflated, which can cause anything from decreased fuel economy to potentially unsafe driving conditions. It conveys the message via a small amber indicator light on the dashboard in the shape of a small tire with an exclamation mark inside.

On some vehicles, like the 2015 Lexus NX, you can find precise tire pressure readouts on the information screen located directly in the instrument cluster.

2015 Lexus NX 200t TPMS


The technology was widely implemented as a response to several auto accidents found to be the direct result of tires not properly being inflated. This is a common occurrence because many drivers don’t regularly check tire pressure, and it’s difficult to gauge the inflation level visually. 


There are two major types of TPMS: 

Indirect: this type utilizes data drawn from wheel speed sensors shared with the anti-lock braking system. By analyzing the rate at which the tires are rotating while the vehicle is moving, if one or more tires falls out of sync with the rest, an alert is triggered. Indirect TPMS is more prone to false alarms because the computer can be tricked by things like unevenly worn tires or tire sizes that don’t match the OEM specifications.

tire pressure monitoring system sensor

Direct: as you might have guessed, the direct method measures air pressure directly from within the tire itself. An embedded sensor sends information to a receiver, programmed to trip the indicator light if the readings from any of the tires fall outside acceptable inflation parameters. Direct TPMS is more accurate than indirect, however require more individual parts that can be expensive and fragile.

Both types require maintenance — the former system needs to be reset each time the tires are inflated or rotated, and the latter runs on non-replaceable batteries (although they do last up to a maximum of 10 years) and require a service shop’s specialized tools to diagnose. 

2015 Lexus NX 200t wheel

Please be aware that TPMS is designed to serve as a visual aid only and shouldn’t be a replacement for checking tire inflation by hand. It’s always a good idea to keep a tire pressure gauge in the vehicle just in case.

Posted by Benjamin Yong

Benjamin Yong is a freelance journalist and communications professional living in Richmond, B.C. He is often found writing about cars and the auto industry, amongst other things, or driving around in his work-in-progress 1990 Mazda MX-5. Twitter: @b_yong Instagram: @popuplights