A Tire Pressure Sensor can be of the direct or indirect type according to the NHTSA legislation. In practice nearly all OE's have opted to install Direct TPMS in their new builds. A direct TPMS is a physical pressure and temperature transducer which is usually either valve stem mounted or banded to the wheel and transmits real time tire pressure information to the driver of the vehicle either via a dashboard display or a tire pressure warning light on the instrument cluster.
The sensors are manufactured by international companies such as Schrader, Siemens, TRW, Pacific, Lear, Beru and others. Aftermarket sensors are now being manufactured by the aforementioned as well as by a number of Chinese and Taiwanese companies. There is no common technical standard (physical, electrical or software protocol) for the sensors and the OE's and suppliers have generated a multitude of sensor designs. The OE's have made great efforts to fit the sensors in the plants to ensure they are at the correct angle when fastening, are correctly torqued using a dynamic torque wrench to ensure that they seal and retain their seal, however, these practices have not yet been adopted in the aftermarket servicing of the TPMS. The OE's also have many electrical tests of the TPMS which have not yet been put into practice in the aftermarket to ensure that systems are properly set up before the vehicle leaves the dealer or tire shop.