The tyre defect indicator RPA is designed to monitor the tyre status while driving. For this purpose, the ABS speed sensors determine the speed of the four wheels independent of each other. A calculation logic stage implemented in the DSC control unit evaluates the received data and makes the corresponding information available to the driver as required thus informing the driver of a possible tyre defect.
The tyre defect indicator consists of the following components:
The main function of the system is to monitor the tyre pressure while driving. The tyre pressure to be monitored is determined by the driver. With the aid of the reset button the driver instructs the system to adopt the current set of wheels with the selected tyre pressure as the set reference.
If the speed of a wheel changes as the result of losing air pressure, the control unit sends a corresponding signal dependent on the pressure deviation to the driver information system (warning lamp and gong).
The RPA system differentiates between 5 operating statuses:
After ”switching on” the ignition and after a self-test, the RPA assumes the ”active” status. If the tyre pressure corresponds to the pressure set by the driver minus a permissible tolerance, no message is issued to the driver.
The signal lamp lights up red and an acoustic signal sounds. The state ”Warning” (pressure drop of approx 30%) indicates that road safety is no longer assured. In the state ”Warning”, it is not possible to run the learning procedure. Pressing the RPA button for 4 seconds resets the RPA to the ”Active” state.
The warning lamp lights yellow. In the ”Inactive” state, all RPA functions are shut down.
The warning lamp lights yellow. The ”Fault” state is created by a sensor fault detected by the DSC control unit or RPA button actuation of more than 120 seconds. With ”Ignition On” as well as on starting diagnosis, the RPA becomes active again and then again reports a fault in the case of a sensor fault or a timeout of the RPA button signal.
The learning status is initiated by pressing the RPA button for 4 seconds. The warning lamp lights up for 12 seconds to confirm the start. The learning procedure must be run every time the tyre inflation pressure is corrected or after a tyre change. The driver is responsible for ensuring the tyre inflation pressure is set correctly. The system cannot carry out a plausibility check. The system is able to detect a reduction in tyre pressure of approx 50% of the cold air pressure after a minimum of 10 minutes. As the learning procedure progresses, the pressure difference detected as a tyre failure reduces to approx. 30%.
The warning lamp flashes yellow. In the case of new DSC control units, all RPA functions are disabled. The RPA system is activated by initiating the learning procedure.
The sensors used by the RPA system are already monitored by the ABS and DSC. The RPA will also signal a fault if the ABS and DSC detect a fault.
The following event triggers an additional entry in the fault code memory: