The ABS module determines the loss of pressure in the tires by calculation using the wheel speed sensors of the ABS system. If a tire loses pressure, its diameter decreases and the speed of the wheel therefore increases.
If the ABS module detects such a loss in pressure, it sends a signal to the instrument cluster via the CAN bus and a warning message is displayed in the driver information system. The warning threshold depends among other things on the dimension of the tires being used, the vehicle operating conditions and the status at the last initialization.
Since neither the absolute tire pressure nor the position of the tire is known, after a tire pressure warning the pressure of all the tires must be checked and the system re-initialized. If necessary, the cause of the loss of pressure must be investigated.