There are three common types of TPMS sensors.
The first type is a sensor that is mounted to the rim as a part of the valve stem. This type of valve TPMS sensor can be identified by checking the valve stem on your wheels for a metal valve with a ferrule nut. These TPMS sensors are common on GM vehicles several other imports including Nissan, Toyota, and Honda. If your vehicle uses this type of sensor, please remember that plastic valve caps must be placed on all the sensors. Using a metal cap or no cap at all will cause the valve core to malfunction and result in the sensor needing to be replaced. TPMS Direct sells valve-type sensors complete and ready for installation.
The second type of sensor is commonly used by Ford. This sensor is attached to a metal band on the inside of the rim and mounted opposite of the valve stem. This band-type TPMS sensor is also sold at TPMS Direct complete (with bandclip) and ready for installation.
The third type is a sensorless tire pressure monitoring system that was used prior to the standardization of TPMS due to the TREAD act. To ensure proper tire pressure, this system measures the rolling diameter of each wheel. This type of TPMS is now considered inefficient due to problems with tred wear, aftermarket wheels, different sized tires, and other malfunctions. This sensorless TPMS is common on GM vehicles before the passing of the TREAD act.