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:
Cup holder in the rear seat armrest
Do not sit on or support your body weight
on the rear seat armrest when it is folded
down, as you could otherwise damage it.
Close the cup holder before folding the
rear seat armrest up. Othe ...
Downhill gradients
On long and steep gradients, you must
reduce the load on the brakes by shifting
early to a lower gear. This allows you to take
advantage of the engine braking effect and
helps avoid overheatin ...