Types of TPMS Valves
Types of TPMS
There are two types of system: the indirect TPMS and the direct TPMS.
This type of pressure monitoring system is linked to the ABS of the car to evaluate an approximative pressure in the tires. This principle is based on the fact that if a tire has a flat or a leak, its overall diameter will be smaller, making its speed increasing compared to the correctly inflated tires of the car. Since they do not measure the pressure directly but estimate it through other data, those systems are considered indirect TPMS. It is the on-board computer that is evaluating if a tire is deflated and the warns the driver. Note they cannot give accurate data in real-time and they rely on the pressure of one tire compared to the other.
Once a tire is being re-inflated correctly after a deflation, it takes about 20 to 60 minutes of driving before the computer relearns the new parameters of the sensors.
Direct TPMS can measure the exact pressure in each tire because of individual sensors placed directly in the four tires. As opposed to the indirect TPMS, it can have a precise value on not only the tire pressure but also the temperature inside, to prevent over-heating. As soon as there is something irregular, the information is transmitted to the driver through the car’s computer.
Because the direct TPMS is separated from the computer or the car, it can work with batteries or by a system of electromagnetic induction creating electricity. In addition to solving the battery short life, induction allows the TPMS to generate information faster and it decreases the weight of the sensors. This being said, since they are located outside the vehicle, the sensors are more vulnerable to be broken by a big impact, leading to the deprogramming of the sensor if the impact is too important.
Original vs Universal Sensors
Those sensors are preprogrammed with the specific parameters of the car they were made for. Since they are specific, if garages want to provide some to their customers, they need to store many different types of TPMS, for all the manufacturers, for each vehicle model, by sets of four. For this reason, the majority is selling aftermarket universal TPMS sensors, which can be programmed for almost any vehicle.
As mentioned above, universal sensors are all the same: same shape, going at the same place, but they are offered in two different versions, 433 Mhz or 315 Mhz, depending on what frequency the car is using. Universal sensors TPMS are sensors connected to standard tire valves.
Before the installer gets the tire mounted on the wheel, he programs the TPMS sensors with a machine by entering the vehicle information on which they will be installed. Once the sensors are programmed, they are ready to be linked to the vehicle.
The on-board computer now needs to ‘understand’ the new codes generated by the TPMS newly programmed sensors but not all cars have the same relearning process for TPMS codes. Some cars are going to make that recognition by themselves by driving a few kilometres, some will need a manual procedure (a specific combination of ignition, clutch and even horn actions), whereas some other companies, such as Toyota, Lexus or Honda for say, some universal TPMS need a special programming tool to link the car and the sensors.
At PMCtire, we are using ITM universal TPMS, which may require the installation tool called OBD II. It is important when buying universal TPMS, to go to a garage that is working with the proper tools to make the connection possible. Most dealers are not equipped to deal with aftermarket TPMS, so because they just cannot make the computer recognize the codes, they may tell to the costumers that their tires do not have the right TPMS sensors or that they are defective.
Read the TPMS Syncing section for more details about this topic.