A common message with Mercedes-Benz, Blind Spot Assist is a safety feature that warns the driver if another car is in the blind spot–a position that a driver can not see. This feature has been optional in many Mercedes-Benz models since early 2010. Blind Spot Assist gets deactivated typically during heavy rain or drive-through a flooded road. You may also get other warning on the dashboard like: Pre-Safe Functions Limited, Active Lane Keep Assist Unavailable and BAS and ESP lights on. Aside from water, there are other causes that triggers this warning, which are listed below.

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https://www.spotdem.com/2020/11/03/blind-spot-assist-inoperative/