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The Hood Magazine

What is a Tire Pressure Monitoring System?

Dec 05, 2020 10:18AM ● By Discount Tires

Byline: Discount Tire 

For most of us, starting our cars in the morning is a stress-free task. The car’s dashboard typically lights up with warning symbols, but the lights turn back off after a moment. Sometimes, one of the lights on the dash stays on, indicating that something is wrong. 

One of those lights is the tire pressure monitoring system, or TPMS. This light is there to alert the driver that the car’s tires need attention. Additionally, the TPMS can help the driver address changes in temperature, which cause fluctuations in tire pressure. Knowing about the function of the TPMS and keeping tires properly inflated can increase fuel efficiency, extend tire life and contribute to your vehicle’s stability and safety. 

Direct and Indirect TPMS 

The types of TPMS can vary by the system a vehicle is equipped with; direct or indirect. Each type of system uses different mechanical setups and methods to monitor tire pressure and alert the driver when the air pressure is low. 

Direct TPMS measures air pressure through dedicated sensors attached to the wheel. The sensors directly read the pressure in each tire and transmit the data to the vehicle computer. If a tire’s pressure drops below 25% of the recommended inflation from the vehicle manufacturer, the system will activate the dashboard light. This process gives a direct TPMS a greater degree of accuracy than indirect TPMS. 

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. The sensors 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 has low pressure, it will illuminate the dashboard light to alert the driver. 

While the direct TPMS has a variety of sensors that are each designed for specific vehicles and trained to communicate with the car’s onboard computer, the indirect TPMS cannot tell the driver which tire needs inflation. Therefore, it will need to be reset after any service, including a tire change or air pressure adjustment, to ensure system accuracy. 

TPMS Sensor Batteries 

TPMS batteries last approximately six to ten years or 90,000 to 120,000 miles. The battery inside the TPMS sensor is not removable, so a new sensor is required when the battery life has come to an end. If one of the batteries in the TPMS has expired, a replacement will need to be installed by a tire professional so that the system can be trained to recognize the new sensor.  

While the TMPS provides valuable assistance in monitoring a vehicle’s tire pressure, it should never replace a monthly air pressure check.