Energy Capacitor
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2000 BMW Z3, 2000 BMW 328i, 2000 BMW 323i, 1999 BMW Z3, and 1999 BMW M3. However, it is still accessible from the selected car via links, so may be relevant.
If normal power source (battery voltage) is interrupted during a collision, energy capacitor inside SRS control unit supplies SRS power. If energy capacitor fails, a code sets.