When your tyre can lose the pressure slowly we will check the rubber core first. If the core can keep the air, we check the valve stem. If it seems fractured we take off the tyre, clean the valve seat and fit the new valve.
When your car fitted with Tyre Pressure Monitoring System (TPMS) and this system noticed you about any sensors can not communicate, you need to buy a new valve fitted with this sensor. We can replace the old valve.
After the change we need to balancing the wheel because the tyre and rim can rotate relative to each other and the share of the weights will change.
These are the simple parts of the wheel. One spring, one sealing rubber ring, and the outer part with screw thread. Anybody can remove or fit them with a suitable “screwdriver”. But be careful! It can “fly out” because high pressure in the tyre.
This is the most complicated part of the wheel. It has more electronics like a pressure sensor and a bluetooth for communication with the board computer (or ECU). The most of sensor made with built in battery. They cannot be charged from outside and they will be depleted over time and cannot be replaced, therefore in this case you need to buy a new one. The valve replacement is the professionals task. The well equipped services can reading or duplicating and teaching the valves. And the best specialists can communicate with the board computer during the process in case brand new factory valves fitting.
Nobody think that lose the valve cover plastic can cause more problems. But the dust or water entering the valve can destroy the air sealing ability of valve core. In worst case the water will cause a kind of corrosion between the valve stem and valve core. When it happens we can not remove the core, and need to do a complete valve replacement even if the battery is good.