TSB: Mercedes-Benz SOS Fault

The bulletin addresses an issue where the emergency call system displays an 'SOS nonfunctional' message intermittently, especially after extended parking. A software update to the N112/9 control unit restores proper operation, with the system remaining functional during testing.
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June 16, 2026
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Mercedes-Benz SOS Fault

This bulletin applies to all Mercedes-Benz vehicles equipped with SA code 360/362 emergency call system. The “SOS nonfunctional” message may display intermittently in the instrument cluster. Fault code B129C00 is stored in the control unit log. The message usually occurs after the vehicle has been parked for an extended period of time (5 or more days). The message disappears after a few minutes. The emergency call system is functional when tested.

The cause: software in N112/9 control unit for telematics services (HERMES). Perform a software update for control unit N112/9 to software release E522.7.

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