Mercedes-Benz E-Class Sedan Operator's Manual page 436

434 Display messages and warning/indicator lamps
Driving systems
Warning/indicator lamp
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Distance warning lamp
Possible causes/consequences and
The red distance warning lamp lights up while the vehicle is in motion.
The distance to the vehicle in front is too small for the speed selected.
If there is an additional warning tone, you are approaching an obstacle at too high a speed.
Be prepared to brake immediately.
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Increase the distance.
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Active Brake Assist .
M Solutions