What is TPMS?

TPMS stands for Tire Pressure Monitoring System. The purpose of the tire pressure monitoring system in your vehicle is to warn you that one or more tires are significantly under-inflated, possibly creating unsafe driving conditions. The TPMS low tire pressure indicator is a yellow symbol that illuminates on the dashboard instrument panel in the shape of a tire cross-section with an exclamation mark. There are two different kinds of TPMS systems, direct and indirect.
An indirect TPMS typically relies on wheel speed sensors that the anti-lock brake system uses. So, an indirect tire pressure monitoring system doesn’t actually measure tire pressure.  Instead, an indirect tire pressure monitor simply measures how fast your tires are rotating and sends signals to the computer that will actuate the indicator light when something in the rotation seems out of the ordinary. A direct system uses pressure indicators inside each wheel. It is the decision of the car manufacture which system to use, but all modern cars need to have one.