BMW (SRS) Self Diagnostic System

FUNCTION OF FAILURE WARNING LAMP
As of terminal R (ignition lock position 1), the failure warning lamp begins to light for approx. 6 seconds and then goes out indicating that the airbag system is in standby mode. If a defect occurs in the airbag system, the failure warning lamp begins to flash for approx. 60 seconds and then lights with a steady light. This shows the driver that the airbag system is not in standby mode. The airbag system does not resume standby mode until the defect is rectified and the trouble code memory in the diagnostic unit has been cleared.

DEFECT DETECTION
While in standby mode the Supplemental Restraint System (SRS) control module constantly monitors the system for defects. Depending on the type of defect, faults must be applied for a certain period of time (200 ms to 80 sec) in order to be detected and stored as a trouble code. If a trouble code is stored, the airbag system remains out of operation until the trouble code is cleared by an external diagnostic unit (BMW DIAGNOSTIC SYSTEM, BMW MoDiC, airbag diagnostic reset tool or compatible tester). The control module, however, still continues to monitor the system.

If the defect conditions no longer exist while diagnosis is being performed, the defect is indicated as a long-term defect.

If the defect no longer exists, the type of defect is changed to an intermittent defect. The trouble code, however, still remains in the trouble code memory.

Intermittent Codes
Following trouble code retrieval, a message will appear on the BMW service tester, indicating whether the first trouble code was detected within the last sixty minutes. This message enables the determination of whether a trouble code is intermittent or if it was caused by removal of the steering wheel or instrument cluster when the airbag system is in standby mode

Measuring the relevant defect path of an intermittent trouble code is of little use since the defect no longer exists at the time the test is carried out. In the case of wire defects, troubleshooting should be carried out in accordance with the instructions provided on the display screen. Wherever possible, the complete wire as well as all plug connections on the defect path should be visually inspected. Repair or renew any pinched wires and defective or loose plug connections.

Long-term Defects
In this case, perform troubleshooting as displayed on the screen. If no defect can be found in the periphery, check the disconnected plug connection for dirt and defects and if necessary repair or renew defective parts.