MERCEDES-BENZ S-Class 2008 W221 Comand Manual

730 Practical hintsBatteries!
The consumer battery located in the trunk is
a valve-r
egulated l
ead a
cid (VRLA) battery, also
referred to as “fleece” battery. Such batteries do
not require topping-up of the electrolyte level.
VRLA batteries therefore do not have cell caps
and the battery cover is non-removable. Do not
attempt to open the consumer battery as other-
wise the battery will be damaged.
Even though VRLA batteries do not require top-
ping-up of the electrolyte level and cannot be
opened to check the electrolyte level, the bat-
tery condition must be checked periodically by
performing a battery conductance test. Refer to
Maintenance Booklet for battery condition test-
ing intervals.
As with any other battery, disconnect the con-
sumer battery if you do not intend to operate
your vehicle for an extended period of time to
prevent battery discharge or connect an acces-
sory battery charge unit expressly approved by
Mercedes-Benz for your vehicle model to main-
tain the battery charge. Contact an authorized
Mercedes-Benz Center for further information.
!
The factory-equipped VRLA battery is
leak-proofed. Only use a battery as replacement
that has the same security features and is of
identical size, voltage, and capacity as the facto-
ry-equipped battery.
The battery, the battery ventilation and the later-
al plug must always be securely installed when
the vehicle is in operation.
Warning!
G
Failure to follow these instructions can re-
sult in severe injury or death.
Never lean over batteries while connecting,
you might get injured.
Battery fluid contains sulfuric acid. Do not
allow this fluid to come in contact with eyes,
skin or clothing. In case it does, immediately
flush affected area with water and seek
medical help if necessary.
A battery will also produce hydrogen gas,
which is flammable and explosive. Keep
flames or sparks away from battery, avoid
improper connection of jumper cables,
smoking, etc.Warning!
G
Do not place metal objects on the battery as
this could result in a short circuit.
Use leak-proof battery only to avoid the risk
of acid burns in the event of an accident.
Take care that you do not become statically
charged, e.g. by wearing synthetic clothing
or rubbing against textiles. For this reason,
you also should not pull or push the battery
over carpets or other synthetic materials.
Never touch the battery first. First touch the
outside body of the vehicle in order to re-
lease any possible electrostatic charges.

731 Practical hints
Batteries
Starter battery (example illustration from
S 550)1Negative terminal
2Positive terminal
Disconnecting starter battery
Secure vehicle in place with electronic
parking brake (
page 422).

Shift the automatic transmission to
park positionP (
page 426).
Do not rub the battery with rags or cloths.
The battery could explode if touched due to
electrostatic charge or due to spark forma-
tion.!
Switch off the engine and switch off the ve-
hicle’s internal electrical functions (
page 732)
before you disconnect or remove the battery’s
terminal clamps. You could otherwise destroy
electronic assemblies such as the generator.
Have the battery checked regularly by an autho-
rized Mercedes-Benz Center. Refer to Mainte-
nance Booklet for maintenance intervals or
contact an authorized Mercedes-Benz Center for
further information.
!
Do not connect any consumers directly to
the starter battery. The starter battery will other-
wise be discharged.
i
Only replace a discharged battery with a bat-
tery recommended by Mercedes-Benz. The con-
sumer battery is installed in the trunk in such a
way that it is safeguarded as much as possible
against mechanical destruction in the event of
an accident.
i
Remove SmartKey from starter switch (vehi-
cles with KEYLESS-GO*: Make sure the vehicle’s
on-board electronics have status 0)
(
page 370) when you turn off the engine and
no longer require any electrical consumers. The
vehicle then uses very little power and the con-
sumer battery is spared.
i
If the consumer battery is discharged, you
must use the mechanical key to unlock the vehi-
cle (page 708). Since the vehicle has a sepa-
rate starter battery, however, you can still start
the vehicle.
!
Always disconnect the starter battery in the
order described below. You could otherwise
damage the vehicle’s electronics.
!
Switch off the vehicle’s internal electrical
functions before disconnecting the starter bat-
tery. If the vehicle is stationary for more than one
hour with the SmartKey removed, you do not
need to switch off the vehicle’s internal electrical
functions.

732 Practical hintsBatteriesSwitching off vehicle’s internal
electrical functions
Turn off all electrical consumers.

Turn SmartKey in starter switch to po-
sition 0.

Turn SmartKey in starter switch to po-
sition 1.

Wait for 30 seconds.
The vehicle’s internal electrical func-
tions are switched off.

Turn SmartKey in starter switch to po-
sition 0.Disconnecting starter battery

Open the hood (
page 573).

Use a 10-mm open-end wrench to dis-
connect the battery negative lead.

Remove cover2 (
page 731) from
the positive terminal.

Disconnect the battery positive lead.
Removing starter battery
Pull out the battery ventilation hose
from the battery (depending on battery
arrangement in your vehicle model, the
ventilation hose is located either on the
left or right side of the battery).

Fold bar on starter battery up.

Take out the starter battery.
Charging battery
i
Vehicles with KEYLESS-GO: remove the
KEYLESS-GO button (
page 371) and use the
SmartKey with KEYLESS-GO like a normal
SmartKey.
!
Do not remove the SmartKey!
i
For your convenience, have the starter bat-
tery removed by a Mercedes-Benz Center.
Warning!
G
Never charge a battery while still installed in
the vehicle unless the accessory battery
charge unit approved by Mercedes-Benz is
being used. Gases may escape during charg-
ing and cause explosions that may result in
paint damage, corrosion or personal injury.
An accessory battery charge unit specially
adapted for Mercedes-Benz vehicles and
tested and approved by Mercedes-Benz is
available, permitting the charging of the bat-
tery in its installed position. Contact an au-
thorized Mercedes-Benz Center for
information and availability. Charge battery
in accordance with the separate instruc-
tions for the accessory battery charger.i
Have the batteries charged by a
Mercedes-Benz Center. If you charge the batter-
ies yourself, follow the operating instructions for
your charging device.

733 Practical hints
Batteries
Starter battery
Connect the switched-off charging de-
vice to the terminals of the starter bat-
tery. Observe the operating
instructions in the manual for the
charging device while doing so.
Reinstalling starter battery
Install starter battery in engine com-
partment.

Swing retaining bar down.
Reconnecting starter battery

Make sure that the consumer battery in
the trunk is correctly installed and con-
nected.

Turn SmartKey in starter switch to po-
sition 0 and remove.

Connect the positive lead and fasten its
cover2 (
page 731).

Connect negative lead1
(page 731).

Attach ventilation tube.

Switch on the ignition (
page 370).

Start the engine (
page 416).

Check vehicle functions.
!
Only use charging devices with a maximum
charging voltage of 14.8 V.
Warning!
G
During the charge procedure, there is a risk
of acid burns due to gases escaping from
the battery. Do not bend over the battery
during the charge procedure.
!
The battery and the battery ventilation hose
must always be securely installed when the vehi-
cle is in operation.
!
Always connect the starter battery in the or-
der described below. Otherwise, the vehicle’s
electronics could be damaged.
Warning!
G
Do not drive without a properly installed and
connected consumer battery.
Have any work on the consumer battery car-
ried out by an authorized Mercedes-Benz
Center.
!
Never invert the terminal connections.
!
Make sure that the battery has a plug where
the ventilation tube is attached to it.

734 Practical hintsJump starting
If the starter battery is discharged, the en-
gine can be started with jumper cables and
the battery of another vehicle. Observe the
following:

Jump starting should only be performed
when the engine and catalytic convert-
er are cold.


Do not start the engine if the battery is
frozen. Let the battery thaw out first.


Only use 12-volt battery to jump start
your vehicle. Jump starting with a high-
er voltage battery could damage the ve-
hicle’s electrical system, which will not
be covered by the Mercedes-Benz Lim-
ited Warranty.


Only use jumper cables with sufficient
cross-section and insulated terminal
clamps.


Always make sure that the jumper ca-
bles are not on or near pulleys, fans or
other parts that move when an engine
is started or running.
Warning!
G
Failure to follow these directions will cause
damage to the electronic components, and
can lead to a battery explosion and severe
injury or death.
Never lean over batteries while connecting
or jump starting, you might get injured.
Battery fluid contains sulfuric acid. Do not
allow this fluid to come in contact with eyes,
skin or clothing. In case it does, immediately
flush affected area with water, and seek
medical help if necessary.
A battery will also produce hydrogen gas,
which is flammable and very explosive. Keep
flames or sparks away from battery, avoid
improper connection of jumper cables,
smoking, etc.
Attempting to jump start a frozen battery
can result in it exploding, causing personal
injury.
Read all instructions before proceeding.
!
Do not tow-start the vehicle.
!
Jump starting should only be performed on
the starter battery installed in the engine com-
partment.
Avoid repeated and lengthy starting attempts.
Do not attempt to start the engine using a bat-
tery quick charge unit.
If engine does not run after several unsuccessful
starting attempts, have it checked at the nearest
authorized Mercedes-Benz Center.
Excessive unburned fuel generated by repeated
failed starting attempts may damage the catalyt-
ic converter and may present a fire risk.
Make sure the jumper cables do not have loose
or missing insulation.
Make sure the cable clamps do not touch any
other metal part while the other end is still at-
tached to a battery.

735 Practical hints
Jump starting
Jump starting should only be performed on
the starter battery. The starter battery is
located in the engine compartment on the
passenger side (
page 731).

Make sure the two vehicles do not
touch.

Secure vehicle in place with electronic
parking brake (
page 422).

Shift the automatic transmission to
park positionP (
page 426).

Turn off all electrical consumers, ex-
cept hazard warning flashers or work
lights.

Open the hood (
page 573).

Start the engine of the vehicle with the
charged battery and run at idle speed.1Positive terminal of your vehicle’s
battery
2Positive terminal of other vehicle’s
battery
3Negative terminal of other vehicle’s
battery
4Negative clamp
Warning!
G
Keep flames or sparks away from battery.
Do not smoke.
Observe all safety instructions and precau-
tions when handling automotive batteries
(page 729).
i
Vehicles with KEYLESS-GO*: remove the
KEYLESS-GO button (
page 371) and use the
SmartKey with KEYLESS-GO like a normal
SmartKey.


736 Practical hintsJump starting
Remove red cover from positive
terminal 1.

Connect positive terminal2 of the
charged battery with positive
terminal1 of the discharged battery
with the jumper cable. Clamp cable to
charged battery2 first.

Connect negative terminal3 of
charged battery to jumper cables and
attach other end4 to a suitable
ground point on the vehicle.

Get into vehicle and start engine within
30 seconds.
If the starting attempt does not suc-
ceed: 
Turn the SmartKey in starter switch
to position 0.

Take out the SmartKey.

Turn off engine of donor vehicle, re-
start it and let it run at idle speed
for several minutes.

Disconnect the jumper cable during
this time.

Reconnect jumper cable as de-
scribed before.

Restart engine.

While the engine is running, switch off
several electrical consumers such as
the blower.

Disconnect jumper cables first from
ground point4 and negative
terminal3, then from positive
terminals1 and2.

Have the battery checked at the near-
est authorized Mercedes-Benz Center.
!
Never invert the terminal connections.


737 Practical hints
Towing the vehicle
Towing the vehicle
Mercedes-Benz recommends that the
vehicle be transported with all wheels off
the ground using flatbed or appropriate
wheel lift/dolly equipment. This method is
preferable to other types of towing.
When circumstances do not permit the
recommended towing methods, the
vehicle may be towed with all wheels on
the ground or front wheels raised (except
vehicles with 4MATIC) only so far as neces-
sary to have the vehicle moved to a safe
location where the recommended towing
methods can be employed.!
To prevent damage during transport, do not
tie down vehicle by its chassis or suspension
parts.
!
Before towing the vehicle observe the fol-
lowing instructions:


Do not tow-start the vehicle.


Use flatbed or wheel lift/dolly equipment
with the ignition switched off.


Do not tow with sling-type equipment. Tow-
ing with sling-type equipment over bumpy
roads will damage radiator and supports.


Towing of the vehicle should only be done
using the properly installed towing eye bolt.
Never attach a tow cable, tow rope or tow
rod to the vehicle chassis, frame or suspen-
sion parts. For more information see “Install-
ing towing eye bolt” (
page 740).
i
If the battery is disconnected or discharged


the SmartKey will not turn in the starter
switch


the automatic transmission will remain
locked in park positionP.
For more information see “Batteries”
(
page 729) or “Jump starting” (
page 734).

738 Practical hintsTowing the vehicleTowing with front wheels raised

Vehicles with KEYLESS-GO*: Remove
the KEYLESS-GO start/stop button
from the starter switch (
page 371).

Insert the SmartKey into the starter
switch.

Switch on the ignition.

Switch off the automatic central lock-
ing (
page 267).

Depress the brake pedal.

Shift the automatic transmission to
neutral positionN.

If engaged, manually release the
electronic parking brake.

Switch off the ignition and leave the
SmartKey in the starter switch.
!
Vehicles with 4MATIC:
Do not tow with one axle raised. Doing so could
damage the transfer case, which is not covered
by the Mercedes-Benz Limited Warranty.
All wheels must be on or off the ground. Observe
instructions for towing the vehicle with all
wheels on the ground (
page 739).
Warning!
G
When leaving the SmartKey or SmartKey
with KEYLESS-GO* in the starter switch, do
not leave children unattended in the vehicle.
It is possible for children to switch on the
ignition which could result in unsupervised
use of vehicle equipment. Unsupervised use
of vehicle equipment could result in an
accident and/or serious personal injury.
!
Keep in mind that it is important for the
SmartKey to be left in starter switch with the ig-
nition switched off. As soon as the SmartKey is
removed from the starter switch the automatic
transmission will shift to park positionP.
!
Make sure that the ignition is switched off.
If the starter switch is in position2, active brak-
ing action through the ESP
® may otherwise seri-
ously damage the brake system.
!
The vehicle may be towed only for distances
up to 30 miles (50 km) and at a speed not to ex-
ceed 30 mph (50 km/h).

739 Practical hints
Towing the vehicle
Towing with all wheels on the ground

Switch on the ignition.

Shift the automatic transmission to
neutral positionN.

If engaged, manually release the
electronic parking brake.
Warning!
G
If circumstances require towing the vehicle
with all wheels on the ground, always tow
with a tow bar if:

the engine will not run


there is a malfunction in the brake
system


there is a malfunction in the power sup-
ply or in the vehicle’s electrical system
This is necessary to adequately control the
towed vehicle.
Prior to towing the vehicle with all wheels on
the ground, make certain the SmartKey is in
starter switch position2.
Warning!
G
With the engine not running, there is no
power assistance for the brake and steering
systems. In this case, it is important to keep
in mind that a considerably higher degree of
effort is necessary to brake and steer the ve-
hicle. Adapt your driving accordingly.
!
Keep in mind that it is important to have the
ignition switched on. As soon as the SmartKey is
removed from the starter switch or the SmartKey
with KEYLESS-GO* is removed from the vehicle,
the automatic transmission will shift to park
positionP.
!
The vehicle may be towed only for distances
up to 30 miles (50 km) and at a speed not to ex-
ceed 30 mph (50 km/h).
i
To signal turns while being towed with the
hazard warning flasher in use, the ignition must
be switched on. You can then activate the com-
bination switch for the left or right turn signal in
the usual manner – only the selected turn signal
will operate.
Upon canceling the turn signal, the hazard warn-
ing flasher will operate again.