TSB: Mercedes-Benz SOS Glitch

This bulletin applies to all 2023 Mercedes-Benz models with an SA code (E350 and others). The “SOS nonfunctional” (emergency call system) message may display intermittently in the instrument cluster. Fault code B129C00 may be stored in the control unit log. The message usually occurs after the vehicle has been non-operational for an extended period of time (5 or more days). The message may disappear after a few minutes following startup.  When tested, the emergency call system appears functional.

The cause is software in the N112/9 control unit for telematics services (HERMES). To remedy, perform a software update to release E522.7.