Mercedes-Benz 2016 GL Operator's Manual page 263

Driving systems
261
Press LOW RANGE button :.
X
Indicator lamp ; flashes.
When the gear change is complete, indica-
tor lamp ; goes out. In the multifunction
display, the LOW RANGE Off message
appears and status indicator = goes out.
While indicator lamp ; is flashing, you can
cancel the gear change by pressing LOW
RANGE button : again.
Z