Parts of TPMS Sensors | Valve Stem, Sensors & Battery

A Tyre Pressure Monitoring System (TPMS) is made up of two primary components: the display monitor and the tyre pressure sensors. The display monitor provides real-time tyre pressure and temperature information to the driver. The sensors mounted on each wheel continuously measure tyre conditions and then transmit the data wirelessly to the display.

While most people focus on the display itself, the sensors are the heart of the system. Each sensor contains several critical components that work together to accurately monitor tyre pressure and alert the driver when a problem occurs.

TPMS sensors generally fall into two categories: internal sensors and external sensors. Internal sensors are mounted inside the tyre - typically replace the standard valve stem. External sensors, on the other hand, screw directly onto the tyre valve stem and can be installed easily DIY.

Although both sensor types perform the same basic function, their construction and individual components differ.

External Sensor Parts

Casing

The casing is the outer shell that holds all internal components and shields them from the external environment. Most quality TPMS sensors use durable plastic or lightweight metal housings that are designed to withstand years of exposure to the elements. The casing is typically sealed with rubber O-rings or gaskets to achieve a high level of water and dust resistance.

Pressure and Temperature Sensors

Inside the casing is a pressure sensor, which continuously measures the air pressure within the tyre. Many modern TPMS sensors also incorporate a temperature sensor, allowing the system to monitor tyre temperature as well. These sensors take frequent readings and provide the raw data.

Electronics

The electronics act as the brain of the TPMS sensor. This circuit board processes information from the pressure and temperature sensors, converts it into digital data and prepares it for wireless transmission.

Battery

External TPMS sensors are powered by a small replaceable battery, commonly a coin-cell battery such as a CR1632 for passenger vehicle systems.

The battery supplies power to the sensors, electronics and wireless transmitter. One of the advantages of external sensors is that the battery can usually be replaced when it reaches the end of its life - allowing the sensor to continue operating without replacing the entire unit.

Screw-On Valve Connection

The bottom of the external sensor contains a threaded screw-on valve connection that attaches directly to the tyre's existing valve stem. This design allows the sensor to be installed in seconds without removing the tyre.

When the sensor is screwed onto the valve stem, a small internal pin depresses the valve core, allowing tyre pressure to reach the sensor chamber for measurement. Rubber seals inside the sensor help create an airtight connection and prevent air leaks.

Internal Sensor Parts

Internal TPMS sensors perform the same function as external sensors but are mounted inside the tyre. Because they are protected within the wheel, they are less exposed to theft, accidental damage and environmental conditions.

Casing

The casing houses and protects the sensitive electronic components within the TPMS sensor. The casing is sealed to prevent moisture and contaminants from reaching the electronics.

Pressure and Temperature Sensors

The pressure sensor continuously measures the air pressure while the temperature sensor monitors tyre temperature - both from inside the tyre. This makes them slightly more accurate since they’re less exposed to external interference.

Electronics

The electronic circuit board receives data from the pressure and temperature sensors, processes the information and transmits it wirelessly to the vehicle's TPMS display.

Battery

Internal TPMS sensors are powered by a sealed lithium battery that is permanently integrated into the sensor assembly. Unlike most external TPMS sensors, the battery cannot be replaced when it reaches the end of its service life.

The battery is designed to last for many years, with OEM and aftermarket internal sensors typically achieving a lifespan of 5 to 10 years depending on usage and driving conditions. Once the battery is depleted, the entire sensor must be replaced and reinstalled inside the tyre.

Valve Stem

The valve stem is an integral part of most internal TPMS sensors. It actually replaces the existing valve stem on your tyres. Thus it becomes the point where your tyres will be inflated/deflated.

Depending on the design, the valve stem may be made from metal or rubber and is secured through the wheel rim. The sensor body is attached to the base of the valve stem inside the tyre, allowing it to directly measure the pressure and temperature of the air within the tyre.