Function
Function
Tire pressure monitoring system (TPMS)
The system contains the central electronic module (CEM)(4/56), Remote Receiver Module (RRX) (4/119) (or remote keyless entry (RKE) if the function for keyless function is installed) and sensors mounted in the wheels. The sensors in the wheels are activated when the vehicle exceeds 40 km/h (25 mph). The sensors then start transmitting data messages approximately once every minute, which are received by the receiver. The signals are then transmitted onwards to the central electronic module (CEM). These messages contain information about the identity number of the sensor and the air pressure of each tire.
The transmitting frequency of the sensors is the same for all sensors. The control module can receive signals from other vehicles with the same system installed. Therefore, the ID number in each sensor is unique. The sensors that are mounted on the actual vehicle are determined via a statistical elimination procedure in the central electronic module (CEM).
When the ignition is switched on the Remote Receiver Module (RRX) (Remote Keyless Entry (RKE) if the keyless function is installed) starts to listen for messages from the sensors. The signals transmit the receiver to the Central electronic module (CEM).
The control module registers the ID numbers that are in the received messages, which the sensors transmit, both from the actual and from other vehicles. All ID numbers that are received are placed in a list in the central electronic module's (CEM) internal memory. For each ID number that is received, the number of times that ID number is received is stored as well.
Because the number of received ID numbers increases, an evaluation of which ID numbers were received the most times is carried out. The ID numbers received the most times receive the highest "rank" and are then considered to belong to the actual vehicle. In this way, there is differentiation between any ID numbers that have been received from other vehicles with the same type of system, which have, for example, been driven in another lane next to the actual vehicle.
This evaluation takes a maximum of approximately 10 minutes if the Central electronic module (CEM) 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.
There are programmed tables in the central electronic module (CEM) containing the recommended air pressure for that vehicle model. The information about the air pressure in the tires found in the messages transmitted from the sensors, is compared with the programmed values in the central electronic module (CEM). If the pressure, which was reported from a sensor, deviates too much from the recommended value a warning message is displayed in the driver information module (DIM) (5/1).
There are two warning levels that generate different warning messages, one warning for low pressure and a warning for very low pressure.
A message is also displayed if a sensor stops transmitting or receives insufficient battery voltage.
A warning lamp also lights in the Driver information module (DIM) at the same time as the warning message appears.
The easiest way to reset a warning is to stop the vehicle, fill the tire with low pressure with air. The warning in the Driver information module (DIM) disappears the next time the ignition is switched on.
If air is filled in a tire that has warned of low pressure and the ignition is on during the entire process, the warning will go out as soon as the pressure in the tire exceeds the normal level.
If a sensor must be replaced for a tire that has warned of low pressure, the system must "learn" the new sensor ID. This can be carried out in different ways:
1. Drive the vehicle faster than 40 km/h (25 mph) for longer than 10 minutes. The warning for low pressure remains in the Driver information module (DIM) until the Central electronic module (CEM) has identified the new sensor.
2. Programming "by hand". This is carried out using the function in VIDA. For more information, see Diagnostic functions.
Note! The vehicle must be parked for longer than 15 minutes to learn the new ID.
Tire pressure messages
