The TPMS will illuminate a dashboard warning light whenever the pressure drops below the vehicle's recommended level by 25% or more. The official TPMS symbol is a yellow exclamation mark inside a tire cross-section. If you see this alert illuminated on the dash, you should immediately check your tire pressure and inspect for punctures.
One of TPMS significant safety advantages is it can help prevent underinflated tires from growing into larger problems. Additionally, the TPMS can help you address changes in temperature that cause fluctuations in tire pressure. Responding to your TPMS and keeping your tires properly inflated can increase fuel efficiency, extend tire life, and contribute to your vehicle’s stability and safety.
TPMS can come in one of two types: direct or indirect. Each type of system uses different mechanical setups and methods to monitor pressure and alert you when pressure is low. Direct TPMS measures air pressure through dedicated sensors in the wheel, while indirect TPMS estimates low pressure based on tire rotation speed.
A direct TPMS uses battery-operated sensors inside the wheel to communicate with the vehicle. The sensors directly read the pressure in each tire and transmit the data to the vehicle computer. The system will trigger the dashboard light if a tire's pressure drops below 25% of the recommended inflation from the vehicle manufacturer. This process gives a direct TPMS a greater degree of accuracy than indirect TPMS. Some advanced direct systems even allow the driver to check individual tire pressures from the dashboard.
An indirect TPMS estimates an underinflated tire through wheel speed sensors used by the anti-lock brake system. These sensors measure the rotational speeds of each tire. They can detect when one tire rotates faster than the others, which means the faster tire is low on pressure. If the system determines that a tire lacks pressure, it will illuminate a dashboard light to alert you.
Automakers developed indirect TPMS to comply with federal regulations while reducing vehicle costs. These systems are cheaper to produce because they utilize existing vehicle components, but they have distinct disadvantages. An indirect TPMS cannot tell the driver which tire needs inflation and needs calibration after any service including a tire change or pressure adjustment to ensure system accuracy
TPMS Sensor Batteries
TPMS batteries last approximately 7-10 years or 100,000 miles. Tire sealant, corrosion from the elements, and a weak or dead battery can make sensor replacement necessary. The battery inside the TPMS sensor is not removeable. When the battery life has come to an end, a new TPMS sensor will be required.
TPMS and Air Pressure Checks
Tire Pressure Monitoring Systems provide valuable assistance in monitoring your tire pressure, but should never replace your monthly air pressure check. Both types of TPMS will only alert you when the tire pressure drops below the vehicle's recommended pressure by 25%. This is a high threshold, as tires underinflated by just 5% begin to suffer from decreased fuel economy, and increased internal temperatures. These issues become more pronounced as underinflation increases, so your tires can be underinflated without triggering a TPMS alert.
For this reason, you should never rely solely on the TPMS to monitor tire pressure. You should always use a reliable gauge to manually check your tire pressure each month. The TPMS should function as a warning that complements your existing routine, not as your first line of defense.
Learn more about Proper Air Pressure.
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