2008 MERCEDES-BENZ GL550 Owner's Manual

368 Operation
Driving instructions

Always secure items in the trailer to
prevent load shifts while driving.

When towing a trailer, check occasion-
ally to make sure the load is secure,
and that lighting and trailer brakes (if
so equipped) are functioning properly.

Take into consideration that when tow-
ing a trailer, the handling characteris-
tics are different and less stable from
those when operating the vehicle with-
out a trailer.
It is important to avoid sudden maneu-
vers.

The vehicle and trailer combination is
heavier, and therefore is limited in ac-
celeration and climbing ability, and re-
quires longer stopping distances.
It is more prone to reacting to cross
wind gusts, and requires more sensi-
tive steering input.

If possible, do not brake abruptly, but
rather engage the brake slightly at first
to permit the trailer to activate its
brake. Then increase the braking force.

If the transmission repeatedly shifts
between gears on inclines, manually
shift to a lower gear (select 4, 3, 2 or 1)
(
page 197).
A lower gear and reduction of speed re-
duces the chance of engine overload-
ing and/or overheating.

On very steep inclines, not manageable
with automatic transmission in1,
switch on off-road driving program
(
page 278) or LOW RANGE mode*
(
page 201).

When going down a long hill, shift into
a lower gear and use the engine’s brak-
ing effect.
Avoid riding the brakes, thus overheat-
ing the vehicle and trailer brakes.

If the engine coolant rises to an ex-
tremely high temperature (coolant tem-
perature needle approaching the red
zone) when the air conditioning is on,
turn off the air conditioning system.
Engine coolant heat can be additionally
vented by opening the windows,
switching the climate control fan speed
to high and setting the temperature
control to the maximum hot position.

Extreme care must be exercised since
your vehicle with a trailer will require
additional passing distance ahead than
when driving without a trailer.
Because your vehicle and trailer is
longer than your vehicle alone, you will
also need to go much farther ahead of
the passed vehicle before you can re-
turn to your lane.
!If the trailer should begin to sway, reduce
the vehicle’s speed immediately.
In no case attempt to straighten out the tow
vehicle and trailer by increasing the speed.
164.boo Seite 368 Freitag, 30. März 2007 12:54 12

369 Operation
Driving instructions
Uncoupling the trailerMake sure the automatic transmission
is set toP (
page 191).
Set the parking brake for the vehicle
(
page 67).
Start the engine (page 56).
Close all doors and the tailgate.
Set the parking brake for the trailer.
Disconnect all electrical plug connec-
tors.
Uncouple the trailer.
Make sure that the trailer coupling is
free of load.
Turn off the engine (page 68).
Warning!G
While you are coupling or decoupling a trail-
er, make sure that you do not

lock or unlock

open or close
a vehicle door or the tailgate.
The vehicle’s level could change and you
could endanger yourself and/or others as a
result.
Make sure that you do not operate the ADS
button* (
page 279) or the vehicle level
control system (
page 279) when cou-
pling/decoupling the trailer.
Warning!G
As soon as you disconnect the electrical
connection between the trailer and the
vehicle, the vehicle will lower. To help avoid
personal injury, make sure no one is near
the wheel housing or underneath the vehicle
before the electrical connection is discon-
nected.
When you uncouple the trailer, the vehicle is
temporarily raised because the springs are
relieved of load. Be especially careful during
this process, as you could otherwise injure
yourself and/or others. Make sure that any
persons remaining in the vehicle do not
press the switches for vehicle level control
or the ADS*.
164.boo Seite 369 Freitag, 30. März 2007 12:54 12

370 Operation
Driving instructions
Passenger compartmentDriving abroad
Abroad, there is an extensive
Mercedes-Benz service network at your
disposal. If you plan to drive into areas
which are not listed in the index of your
Mercedes-Benz Light Truck Center
directory, you should request pertinent
information from an authorized
Mercedes-Benz Light Truck Center.Control and operation of radio
transmitters
COMAND system, radio and telephone*
Warning!G
Always fasten items being carried as secure-
ly as possible.
In an accident, during hard braking or sud-
den maneuvers, loose items will be thrown
around inside the vehicle, and cause injury
to vehicle occupants unless the items are
securely fastened in the vehicle.
The rear cargo compartment is the preferred
place to carry objects. Always use tie down
rings, and if so equipped, always use the
cargo net* when transporting cargo. The
cargo net* cannot secure hard or heavy ob-
jects. Always fasten items being carried as
securely as possible using the cargo
tie-down rings in the cargo floor area and
fastening materials.
Warning!G
Do not forget that your primary responsibili-
ty is to drive the vehicle. Only operate the
COMAND system, radio or telephone
1 if
road, weather and traffic conditions permit.
Bear in mind that at a speed of just 30 mph
(approximately 50 km/h), your vehicle is
covering a distance of 44 feet (approximate-
ly 14 m) every second.
1Observe all legal requirements.
164.boo Seite 370 Freitag, 30. März 2007 12:54 12

371 Operation
Driving instructions
Telephones and two-way radios
Radio transmitters, such as a portable
telephone or a citizens band unit should
only be used inside the vehicle if they are
connected to an antenna that is installed
on the outside of the vehicle.
Refer to the radio transmitter operation
instructions regarding use of an external
antenna.Catalytic converter (gasoline engine)
Your Mercedes-Benz is equipped with
monolithic-type catalytic converters, an
important element in conjunction with the
oxygen sensors to achieve substantial con-
trol of the pollutants in the exhaust emis-
sions. Keep your vehicle in proper
operating condition by following our rec-
ommended maintenance instructions as
outlined in your Maintenance Booklet.
Oxidation catalyst (diesel engine)
Your vehicle is equipped with an oxidation
catalyst, an important element in conjunc-
tion with the oxygen sensors to achieve
substantial control of the pollutants in the
exhaust emissions. Keep your vehicle in
proper operating condition by following
our recommended maintenance instruc-
tions as outlined in your Maintenance
Booklet.
Warning!G
Never operate radio transmitters equipped
with a built-in or attached antenna (i.e. with-
out being connected to an external antenna)
from inside the vehicle while the engine is
running. Doing so could lead to a malfunc-
tion of the vehicle’s electronic system,
possibly resulting in an accident and/or
personal injury.
!To prevent damage to the catalytic convert-
ers, use only premium unleaded gasoline in this
vehicle.
Any noticeable irregularities in engine operation
should be repaired promptly. Otherwise, exces-
sive unburned fuel may reach the catalytic con-
verter, causing it to overheat and potentially
start a fire.
Warning!G
As with any vehicle, do not idle, park or op-
erate this vehicle in areas where combusti-
ble materials such as grass, hay or leaves
can come into contact with the hot exhaust
system, as these materials could be ignited
and cause a vehicle fire.
164.boo Seite 371 Freitag, 30. März 2007 12:54 12

372 Operation
Driving instructions
Emission control
Certain engine systems serve to keep the
toxic components of the exhaust gases
within permissible limits required by law.
These systems, of course, will function
properly only when maintained strictly ac-
cording to factory specifications. Any ad-
justments on the engine should, therefore,
be carried out only by qualified
Mercedes-Benz Light Truck Center autho-
rized technicians.Engine adjustments should not be altered
in any way. Moreover, the specified service
jobs must be carried out regularly accord-
ing to Mercedes-Benz servicing require-
ments. For details refer to the
Maintenance Booklet.
Coolant temperature
During severe operating conditions,
e.g. stop-and-go traffic, the coolant tem-
perature may rise close to approximately
248°F (120°C).
The engine should not be operated with
the coolant temperature above 248°F
(120°C). Doing so may cause serious en-
gine damage which is not covered by the
Mercedes-Benz Limited Warranty.
Warning!G
As with any vehicle, do not idle, park or op-
erate this vehicle in areas where combusti-
ble materials such as grass, hay or leaves
can come into contact with the hot exhaust
system, as these materials could be ignited
and cause a vehicle fire.
Warning!G
Inhalation of exhaust gas is hazardous to
your health. All exhaust gas contains carbon
monoxide (CO), and inhaling it can cause un-
consciousness and possible death.
Do not run the engine in confined areas
(such as a garage) which are not properly
ventilated. If you think that exhaust gas
fumes are entering the vehicle while driving,
have the cause determined and corrected
immediately. If you must drive under these
conditions, drive only with at least one win-
dow fully open at all times.
164.boo Seite 372 Freitag, 30. März 2007 12:54 12

373 Operation
Driving instructions
Warning!G

Driving when your engine is overheated
can cause some fluids, which may have
leaked into the engine compartment to
catch fire. You could be seriously
burned.

Steam from an overheated engine can
cause serious burns which can occur
just by opening the engine hood. Stay
away from the engine if you see or hear
steam coming from it.
Turn off the engine, get out of the vehicle
and do not stand near the vehicle until the
engine has cooled down.
164.boo Seite 373 Freitag, 30. März 2007 12:54 12

374 Operation
At the gas station
Refueling
The fuel filler flap is located on the
right-hand side of the vehicle towards the
rear. Locking/unlocking the vehicle with
the SmartKey or the SmartKey with
KEYLESS-GO* automatically
locks/unlocks the fuel filler flap.1Fuel filler flap
2Fuel filler cap
Turn off the engine.
Vehicles with SmartKey: Remove the
SmartKey from the starter switch.
Vehicles with KEYLESS-GO*: Open the
driver’s door (this puts the starter
switch in position0, same as with the
SmartKey removed from the starter
switch). The driver’s door then can be
closed again.
Warning!G
Gasoline and diesel fuels are highly flamma-
ble and poisonous. They burn violently and
can cause serious personal injury.
Never allow sparks, flame or smoking mate-
rials near gasoline or diesel fuel!
Turn off the engine before refueling.
Whenever you are around gasoline or diesel
fuel, avoid inhaling fumes and skin or cloth-
ing contact, extinguish all smoking materi-
als.
Direct skin contact with gasoline or diesel
fuels and the inhalation of gasoline or diesel
fuel vapors are damaging to your health.
Warning!G
Do not fill diesel tanks with gasoline. Do not
mix diesel fuel with gasoline. Otherwise the
fuel system and engine could be damaged.
In addition, the vehicle could catch fire.
!Damage resulting from mixing gasoline with
diesel is not covered by the Mercedes-Benz
Limited Warranty.
!Diesel engine: When filling the diesel fuel
tank using fuel containers, place a filling filter, a
suede cloth or a clean flannel cloth as a filter.
Otherwise, particles from the fuel container
could clog the fuel lines and/or the diesel injec-
tion system.
iIn case the central locking system does not
release the fuel filler flap, see “Fuel filler flap”
(
page 497).
164.boo Seite 374 Freitag, 30. März 2007 12:54 12

375 Operation
At the gas station
Briefly push on fuel filler flap1 at the
position indicated by the arrow.
Fuel filler flap1 opens slightly.
Open fuel filler flap1 completely.
Turn fuel filler cap2 counterclock-
wise and hold on to it until possible
pressure is released.
Take off fuel filler cap2.
Set fuel filler cap2 on fuel filler
flap1 as shown.
To prevent fuel vapors from escaping
into open air, fully insert filler nozzle
unit.
Only fill your tank until the filler nozzle
unit cuts out – do not top off or over-
fill.
Replace fuel filler cap2 by turning it
clockwise until it audibly engages.
Close fuel filler flap1.
You should hear the latch close shut.
!The fuel filler cap is tethered to the fuel filler
neck. Do not drop the cap. It could damage the
vehicle paint finish.
Warning!G
Overfilling of the fuel tank may create pres-
sure in the system which could cause a gas
discharge. This could cause the gas to spray
back out when removing the fuel pump noz-
zle, which could cause personal injury.
iMake sure to close the fuel filler flap before
locking your vehicle as the flap locking pin
prevents closing after you have locked the
vehicle.
iLeaving the engine running and the fuel cap
open can cause the yellow fuel tank reserve
warning lamp to flash and the ?malfunction
indicator lamp (USA only) or the± malfunc-
tion indicator lamp (Canada only) comes on.
For more information, see “Practical hints”
(
page 439).
iGasoline engine:
Only use premium unleaded gasoline with a min-
imum Posted Octane Rating of 91 (average of
96 RON/86 MON). Information on gasoline
quality can normally be found on the fuel pump.
Please contact gas station personnel in case
labels on the pump cannot be found.
For more information on gasoline, see “Premium
unleaded gasoline (gasoline engine)”
(
page 565), see “Fuel requirements”
(
page 565), and the Factory Approved Service
Products pamphlet (USA only) or contact an
authorized Mercedes-Benz Light Truck Center.
iDiesel engine:
Only use commercially available vehicular
ULTRA-LOW SULFUR HIGHWAY DIESEL FUEL
(15 ppm SULFUR MAXIMUM). Information on
diesel quality can normally be found on the fuel
pump. Please contact gas station personnel in
case labels on the pump cannot be found.
For more information on diesel fuels, refer to the
Factory Approved Service Products pamphlet
(USA only) or contact an authorized
Mercedes-Benz Light Truck Center.

164.boo Seite 375 Freitag, 30. März 2007 12:54 12