TPMS (Tyre Pressure Monitoring System)

Direct systems use a pressure sensor in each wheel; indirect systems use the ABS wheel speed sensors to detect a smaller rolling tyre. TPMS is required on new cars in the US and EU. Direct sensors have batteries that typically last several years and are usually replaced as a unit. New sensors may need to be programmed to the car.

Direct sensors send pressure readings by radio to the car. Indirect systems compare wheel speeds.

A steady TPMS light means check the pressures; a flashing light usually means a system fault. Indirect systems must be reset after inflating. TPMS does not replace regular pressure checks; it only warns when pressure has already dropped significantly.