PS: USA uses 315 MHz, Europe and most of the rest of the world (ROW) uses 433MHz ISM band. So USA sensors cannot be used in Euro vehicles and vice-versa. Likewise, USA rear view mirrors (which contain the TPMS receiver) are either 315MHz or 433MHz for either USA or EUR/ROW respectively.
Tire pressure monitoring system (TPMS)
The tire pressure sensors are installed together with the air valve on the rim. The sensor consists of a pressure sensor, a communication circuit, an acceleration sensor and a battery.
The system covers the upper electronic module (UEM) (4/70) and the sensors in the wheels. The sensors in the wheels are activated when the vehicle exceeds 40 km/h (25 mph). The sensors then start to transmit data messages approximately once per minute, which are received by the remote control receiver in the Upper electronic module (UEM). These messages contain the sensor’s ID number and air pressure in the tire where the sensor is mounted.
The frequency used by sensors to transmit is the same for all sensors. Thus, the control module can receive signals also from other vehicles with the same system installed. However, the ID-number in each sensor is unique.
Sensors installed on your own vehicle can be retrieved by a statistical selection in the Upper Electronic Module (UEM). When the ignition is turned on the Upper Electronic Module (UEM) starts to listen for messages from the sensors. The control module registers the ID-numbers contained in the received messages transmitted by the sensors, both from own and from other vehicles.
All ID-numbers are added in a list in the internal memory by the Upper Electronic Module (UEM). For each received ID-number, the number of times it has been received is also saved. As the quantity of received ID-numbers increases, an assessment takes place of which ID-numbers have been received most times. The four ID-numbers that have been received most often get the highest “ranking” and are then considered to belong to the own vehicle.
In this way any ID-numbers that may have been received from other vehicles with the same type of system, e.g., driving in the adjacent lane, are separated. This assessment takes approx. 5 minutes if the Upper Electronic Module (UEM) is empty of data.
If the evaluation has been carried out, the sensors that are assumed to belong to the actual vehicle are stored in the control module. The information remains between each driving cycle. In this case, it is sufficient for the control module to receive a message from each sensor with corresponding ID number to complete evaluation.
In Upper Electronic Module (UEM), there are tables programmed with the recommended air pressure for this specific vehicle model. This information about air pressure in tires included in messages from sensors is compared to programmed values in Upper Electronic Module (UEM).
If the pressure reported from a sensor differs more than 22% from the recommended value, a warning message will be shown in the Driver information module (DIM).
There are two warning levels that generate different warning messages, one warning for low pressure and one warning for no pressure. A message will also be shown is a sensor should stop transmitting or should receive too low battery voltage.
To reset a warning it is easiest to stop the vehicle and fill air in the tire where the air pressure is low. In order for the warning to reset air has to be filled so that the air pressure reaches a level that corresponds to at least 95% of the recommended air pressure, and then drive the vehicle faster than 40 km/h (25 mph) for more than 10 minutes, accumulated time.
If the customer has come to the workshop, the warning can also be reset by filling air in the tire where the air pressure is low (up to min. 95% of the recommended air pressure) and then the sensor is activated with the special tool for activating the tire pressure sensor.
When air is filled and the pressure changes, the sensor immediately sends a signal to Upper Electronic Module (UEM). If the ignition is on, the warning is reset immediately.
Note! Only applies to USA/CDN. A warning lamp also lights in the Driver information module (DIM) at the same time as the warning message.