The tire defect indicator (RPA) is designed to monitor the tire status while driving. The ABS wheel speed sensors monitor the four wheel speeds independently of one another. The CIM control module evaluates the wheel speed signals of the individual ABS wheel speed sensor and passes this information on to the driver if appropriate. The driver is informed of a possible tire defect.
Control module
The tire defect indicator function is integrated in the Chassis Integration Module (CIM). The CIM control module evaluates the speed signals of the ABS wheel speed sensors. The tire parameter data required for the series is stored permanently in the CIM control module.
ABS wheel speed sensor
The ABS wheel speed sensors provide the wheel speed signals via the DSC control module directly to the CIM control module. Each wheel speed signal is transmitted from the DSC control module to the CIM control module across a separate line.
Soft button
The soft button is integrated in the controller and it is used to standardize the system.
The system is designed to monitor the tire status while driving. Loss of pressure in a tire reduces the rolling circumference of the wheel. This increases the rotation speed of this wheel. The Tire defect indicator measures the wheel speeds and sets up a comparison of the diagonally opposed wheels and the average speed, thus detecting air pressure loss. In this context, extreme driving situations such as strong acceleration or fast cornering are detected and corrected by the software. The system provides information as of 15 km/h minimum speed. The ABS speed sensors determine the wheel speed signals and send them via the DSC control module to the CIM control module. The tire pressure to be monitored is specified by the driver. Using the soft button, the driver instructs the system to adopt the current set of wheels with the selected tire pressure as the set reference. Within the framework of the calibration process, the system automatically learns the tire reference status. Depending on driving style and conditions, the learning process can take between 45 minutes and several hours. However, the system is already armed for warnings after 10 minutes and can detect air pressure losses of 50%. As the calibration continues, the warning thresholds are increased to 30% ± 10% of the cold air pressure. The instrument cluster informs the driver about the operating status of the Tire defect indicator.
Supplementary information: ”With standard tires: Change tires, see Owner's Manual. With safety tires: Continue journey max. 250 km at max. 80 km/h. Have the fault checked by the nearest BMW Service.”
The system has determined a reduction of pressure in a tire that is above the defined values (see function).
Supplementary information: ”Tire monitoring failure! Tire punctures can not be detected. Contact BMW Service at the next opportunity.”
A system malfunction detected by the CIM control module.
Calibration must be performed every time the cold air pressure, the wheel position or the set of wheels are changed. If this is not the case, a false alarm can occur.