Mercedes-Benz 2016 GL Operator's Manual page 121

Therefore, do not switch the seat heating on
repeatedly.
Driver's and front-passenger seat
Rear seats
The three red indicator lamps in the button
indicate the heating level you have selected.
The system automatically switches down
from level 3 to level 2 after approximately
eight minutes.
The system automatically switches down
from level 2 to level 1 after approximately ten
minutes.
The system automatically switches off
approximately 35 minutes after it is set to
level 1.
Turn the SmartKey to position 1 or 2 in the
X
ignition lock ( page 165).
Y
To switch on: press button : repeatedly
X
until the desired heating level is set.
To switch off: press button : repeatedly
X
until all the indicator lamps go out.
i If the battery voltage is too low, the seat
heating may switch off.
Seats
119
Z