A tire pressure monitoring system (TPMS) is an electronic system for monitoring the air pressure in a vehicle tire, triggering a dashboard warning light in the event of an under- or over-inflated tire.
Since 2008, TPMS systems have been required on all new passenger vehicles in the U.S. to alert the driver when a tire is under-inflated by as much as 25%.
The main function of a TPMS sensor is to send data to the vehicle’s ECU or to a specific receiver on the vehicle. In addition to tire pressure, that data might include sensor location, unique sensor ID, temperature, battery life and other diagnostic information. This includes supporting graphical displays that reveal the tire position that requires attention.
On many dashboards, a steady TPMS warning light means the tire pressure is not safe. A flashing light means the TPMS itself needs checked, often due to a low battery. When a TPMS sensor fails, usually the entire sensor unit needs replaced, as batteries are built into the unit itself and not replaceable.
As there is no universal technical standard for TPMS sensors, they do vary by frequency, modulations, data structure, communication protocols, fitment and other factors. Most common fitments to the U.S. are those that measure conditions directly, attached to the base of the valve stem or as a band attached to the rim.
The tire service technician must use a portable TPMS tool to test the TPMS, read the wheel sensor ID and reprogram the car's ECU service work is performed, such as tire repair, tire or wheel replacement, TPMS replacement, tire rotation, etc. The tool also needs to be able to turn off the TPMS warning light once the work has been completed successfully.
In addition to battery failure, the next common reason a TMPS sensor goes bad is due to tire and wheel service. When removing the tire from the wheel using a tire changing machine, be aware of where the tire removal blade is positioned so as not to damage the sensor. Also, check to be sure the replacement sensors are correct as the sensors from different manufacturers look alike and can be confused easily.