On most vehicles, the air pressure is monitored by a sensor inside each tire, which is known as a direct system. The sensor is part of the valve stem assembly and may or may not be detachable. When the diaphragm inside the sensor is pressurized, it sends a radio frequency (RF) signal to a receiver on the vehicle, which calculates the air pressure to determine if it is underinflated by 25% or more when compared to the recommended pressure on the tire placard. There are also a few indirect systems that use the wheel speed sensors, but in either case, any tire that is underinflated by 25% or more will result in some type of warning light on your dashboard or instrument panel.
When the air pressure in one or more of your tires falls below 25% of the recommended inflation for your vehicle, you will see a yellow light that looks like a horseshoe with an exclamation point illuminate on the dashboard. It’s a signal that one or more of your tires might be overloaded, so the best practice is to have them checked immediately by a tire professional. On one hand, it might be that one or more of your tires are a little low on air pressure. On the other, it could be a leak that will eventually result in a flat tire that may need to be replaced or a dangerous tire failure while you are driving. Motorists should never ignore a TPMS warning light because it is a sign that the air pressure may not be enough to support the load of the vehicle and its contents.
It’s also important to know that every TPMS has a built-in mechanism to warn you when the system isn’t monitoring the tires at all. If the light starts blinking on and off for about 90 seconds after turning on the ignition and then stays illuminated, the TPMS has a malfunction. Some car companies also use the yellow letters TPMS to identify a system that is malfunctioning and not monitoring your tires.
If the TPMS has a malfunction, the vehicle must be taken to a tire service professional in order to diagnose the problem. When the TPMS is operating correctly and all of the tires on your car are within 25% of the recommended air pressure, the yellow light will go out shortly after starting the car.
Underinflated tires are visually difficult to detect. TIA recommends that tires are inspected and checked monthly with an accurate gauge. TPMS was never intended to be a substitute for regular tire maintenance.
TPMS notifies you when your vehicle’s tires are low on air. By helping you maintain proper tire pressure, TPMS can increase your safety on the road by decreasing irregular tire wear, improving your vehicle’s handling, reducing braking distance and bettering fuel economy. If ignored, the chances of a tire failing and causing the vehicle to lose control continue to increase each day the tire is low on inflation pressure.
Next to the seatbelt, TPMS is probably the most important safety system on your vehicle. When it’s monitoring the inflation pressure in your tires, you’ll have an added level of confidence that the tires can support the weight of the vehicle and its contents.