Tire Pressure Monitoring System (TPMS)
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 that the sensors transmit on is the same for all sensors. The control module can also receive signals from other vehicles with the same system installed. However, the ID number in each sensor is unique. The sensors that are mounted on the actual vehicle are determined by an elimination procedure in the Upper electronic module (UEM). When the ignition is switched on, the Upper electronic module starts to listen for messages from the sensors. The control module registers the ID number found in the received messages that the sensors transmit, from the actual vehicle and other vehicles. The Upper electronic module stores all ID numbers that are received in a list in its internal memory. For each ID number that is received, the number of times that that ID number is received is also saved. As the number of ID numbers received increases, the ID numbers received the most times are evaluated. The four ID numbers that have been received the most times receive the highest "calculation" and are considered to belong to the actual vehicle. In this way, any ID numbers that have been received from other vehicles can be differentiated. For example, ID numbers that are in another lane next to the actual vehicle. This evaluation takes approximately 5 minutes if the Upper electronic module has no 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 there are tables programmed with which air pressure is recommended for this specific vehicle model. This information about air pressure in the tires included in the messages sent from the sensors is compared to the programmed values in Upper Electronic Module.
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.
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 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 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. If the ignition is on, the warning is reset immediately.
Only applies to USA/CDN. A warning lamp also lights in the Driver information module at the same time as the warning message.