The purpose of the tire pressure monitoring system (TPMS) in your vehicle is to warn you that at least one or more tires are significantly under-inflated, helping you focus on what really matters: your safety and peace of mind while driving.
The TPMS low tire pressure indicator is a yellow symbol that illuminates on the dashboard instrument panel in the shape of a tire cross-section (that resembles a horseshoe) with an exclamation point.
You’ll find two main types of TPMS in vehicles: direct and indirect systems.
An indirect TPMS typically relies on wheel speed sensors that the anti-lock brake system uses. These sensors measure the rate of revolution each wheel is making and can be used by on-board computer systems to compare with each other and to other vehicle operation data such as speed.
Based on the rate of revolution of each wheel, the computer can interpret the relative size of the tires on your vehicle. When a wheel starts spinning faster than expected, the computer calculates that the tire is underinflated and alert the driver accordingly.
So, an indirect tire pressure monitoring system doesn’t actually measure tire pressure. It’s not electronically processing the same kind of measurement you might see with a tire gauge. Instead, an indirect tire pressure monitor simply measures how fast your tires are rotating and sends signals to the computer that will actuate the indicator light when something in the rotation seems amiss.
Direct TPMS uses pressure monitoring sensors within each tire that monitor specific pressure levels – not just wheel revolution data from the anti-lock brake system.
Sensors in a direct TPMS may even provide tire temperature readings. The direct tire pressure monitoring system sends all of this data to a centralized control module where it’s analyzed, interpreted, and, if tire pressure is lower than it should be, transmitted directly to your dashboard where the indicator light illuminates. A direct tire pressure monitor usually sends all of this data wirelessly. Each sensor has a unique serial number. This is how the system not only distinguishes between itself and systems on other vehicles, but also among pressure readings for each individual tire.
Many manufacturers use proprietary technology for these highly specialized systems, so replacing a TPMS in a way that’s consistent and compatible with your vehicle will require an experienced, knowledgeable technician.
Although the methods may be different, both systems serve the same purpose and activate the same indicator light. Even though a TPMS can deliver accurate alerts when properly maintained, it’s not a replacement for manual air pressure checks, consider it just another item in your car maintenance toolbox.
Indirect TPMS relies on wheel speed sensors integrated with ABS technology to detect underinflation. Direct TPMS sensors can be found in two ways—mounted inside the tire either at the base of the valve stem or banded to the wheel’s barrel. Most passenger cars and light trucks use valve-stem sensors, which can be spotted by these features:
Some high-performance vehicles use band-mounted sensors wrapped around the middle of the wheel, built for durability in demanding conditions.
Inside every TPMS sensor, a pressure cavity tracks changes in air pressure in real time, powered by a tiny battery (lasting 5–10 years), microcontroller, RF transmitter, and a temperature sensor. When pressure drops, the sensor transmits this data wirelessly to your vehicle’s computer.
To save battery power, sensors “sleep” when the car is parked and “wake up” with wheel movement. Most transmit new data every 30 to 60 seconds while driving, but may signal more frequently during rapid changes.
Beyond the standard reset after inflating or rotating tires for indirect TPMS, plan to reset your TPMS system when:
Double-check your owner’s manual for your vehicle’s timing and reset instructions so your sensor TPMS keeps working correctly.
That indicator light in your vehicle has a history. It’s a history rooted in years of uncertainty about proper tire pressure and many serious car accidents that might have been avoided had drivers known their air pressure was low. Even now, it’s estimated that a substantial number of vehicles hit the road each day with underinflated tires. However, proper tire maintenance with the aid of a TPMS can and does help prevent many serious accidents.
Before this indicator light became commonplace, knowing whether your air pressure had reached unsafe levels meant getting out, crouching down, and using a tire gauge. With few exceptions, this was the only pressure-checking tool ordinary consumers had at their disposal.
There's never a good time for a flat, and with Bridgestone's innovative solution, you won't have to worry about it. Our DriveGuard tires are masterfully engineered to keep you moving for up to 50 miles at speeds of up to 50 MPH, minimizing disruption and maintaining confidence on the road.
Beyond merely providing peace of mind, Bridgestone DriveGuard tires are designed with advanced run-flat technology and reinforced sidewalls that offer superior durability and reliability.