What system uses sensors to detect low tire pressure and warn the driver?

The system that detects low tire pressure and warns the driver is a Tire Pressure Monitoring System, or TPMS. It helps identify under-inflation before it causes poor handling, excess tire wear, reduced fuel economy, or a tire failure.

There are two principal types. Direct TPMS uses pressure sensors mounted inside the wheels, often as part of the valve stem, and sends measured pressure data to the vehicle. Indirect TPMS uses wheel-speed sensors from the anti-lock braking system: an under-inflated tire changes rolling radius and rotates at a slightly different speed.

A common mix-up is assuming every TPMS sensor directly measures air pressure. Indirect systems estimate pressure and may not display an exact value for each tire. They also usually need to be reset after the tires are correctly inflated or replaced.

TPMS became prominent after tire-safety concerns in the United States, where the TREAD Act led to federal requirements for light vehicles. In the European Union, TPMS became mandatory for new passenger-car registrations from November 2014.