System self-test
The 42 indicator lamp illuminates when you:
• turn the SmartKey to position 1 or 2 in the
ignition lock
• on vehicles with KEYLESS-GO, press the
Start/Stop button once or twice
The 
indicator lamp goes out
again after approximately six seconds.
If the indicator lamp does not
illuminate or is lit continuously, the system is
malfunctioning. Have the BabySmart™
system checked at an authorized Mercedes-
Benz Center before transporting a child on
the front-passenger seat.
For further information, see "Problems with air bag deactivation system".
WARNING 
Do not place powered-on laptops, mobile
phones, electronic tags such as those used in
skipasses or similar electronic devices on the
front passenger seat. Signals from such
devices may interfere with the BabySmart™
air bag deactivation system. Such signal
interference may cause the
indicator lamp not to come on during self-test.
The + SRS indicator lamp and/or the
indicator lamp could be
continuously lit, indicating that the system is
not functioning. The front-passenger front air
bag could deploy inadvertently or fail to
deploy in an accident.
See also:
Installing the ball coupling
WARNING
If the vehicle/trailer combination is not
secured, the trailer may come loose. As a
result, you could cause an accident.
Therefore, make sure that the ball coupling is
secured with th ...
Automatic engine start
The engine is started automatically if you:
- release the brake pedal when HOLD is not
activated and the transmission is in
position D or N
- shift the transmission to position R
...
Storing and maintaining the currentspeed
You can store the current speed if you are
driving faster than 20 mph (30 km/h).
► Accelerate the vehicle to the desired
speed.
► Briefly press the cruise control lever
up 1 or down ...