Mercedes-Benz G-Class Operator's Manual page 186

Driving systems
184
Deactivating/activating PARKTRONIC
Indicator lamp
:
To deactivate/activate PARKTRONIC
;
If indicator lamp : lights up, PARKTRONIC is
deactivated.
i
PARKTRONIC is automatically activated
when you turn the SmartKey to position 2 in
the ignition lock.
Towing a trailer
PARKTRONIC is deactivated for the rear area
when you establish an electrical connection
between your vehicle and a trailer.