ECU MERCEDES-BENZ B-CLASS 2012 Workshop Manual

X
Open the tailgate.
X Lift the cargo compartment floor up
(Y page 246).
i Towing eye ; is located under tire
inflation compressor :.
Vehicles with a tire-change tool kit X
Open the tailgate.
X Lift the cargo compartment floor up
(Y page 246).
X Remove the tire-change tool kit.
The tire-change tool kit contains:
R Jack
R Lug wrench
R One pair of gloves
R Folding wheel chock Flat tire
Preparing the vehicle
Your vehicle may be equipped with:
R MOExtended tires (tires with run-flat
properties) ( Y page 281)
Vehicle preparation is not necessary on
vehicles with MOExtended tires.
R a TIREFIT kit (Y page 280)
Information on changing/mounting a wheel
(Y page 319).
X Stop the vehicle on solid, non-slippery and
level ground, as far away as possible from
traffic.
X Switch on the hazard warning lamps.
X Secure the vehicle against rolling away
(Y page 149).
X If possible, bring the front wheels into the
straight-ahead position.
X Switch off the engine.
X Remove the SmartKey from the ignition
lock. X
All occupants must get out of the vehicle.
Make sure that
they are not endangered as
they do so.
X Make sure that no one is near the danger
area while a wheel is being changed.
Anyone who is not directly assisting in the
wheel change should, for example, stand
behind the barrier.
X Get out of the vehicle. Pay attention to
traffic conditions when doing so.
X Close the driver's door.
i Vehicles equipped with

MOExtended tires
are not equipped with a TIREFIT kit at the
factory. It is therefore recommended that
you additionally equip your vehicle with a
TIREFIT kit if you mount tires that do not
feature run-flat properties, e.g. winter tires.
A TIREFIT kit can be obtained from a
qualified specialist workshop. MOExtended tires (tires with run-flat
properties)
General notes With MOExtended tires (tires with run flat
characteristics), you can continue to drive
your vehicle even if there is a total loss of
pressure in one or more tires. The affected
tire must
not

show any clearly visible damage.
You can recognize MOExtended tires by the
MOExtended marking which appears on the
sidewall of the tire. You will find this marking
next to the tire size designation, the load-
bearing capacity and the speed index
(Y page 313).
MOExtended tires may only be used in
conjunction with an active tire pressure loss
warning system.
If the pressure loss warning message
appears in the multifunction display:
R Observe the instructions in the display
messages ( Y page 219).
R Check the tire for damage.
R If driving on, observe the following notes. Flat tire
281
Breakdown assistance
ProCarManuals.com

necessary for you to disconnect the battery
yourself, make sure that:
R
you switch off
the engine and remove the
SmartKey. Check that all the indicator
lamps in the instrument cluster are off.
Otherwise, electronic components, such
as the alternator, may be damaged.
R you first remove the negative terminal
clamp and then the positive terminal
clamp. Never swap the terminal clamps.
Otherwise, the vehicle's electronic
system may be damaged.
R on vehicles with automatic transmission,
the transmission is locked in position P
after disconnecting the battery. The
vehicle is secured against rolling away.
You can then no longer move the vehicle.
The battery and the cover of the positive
terminal clamp must be installed securely
during operation.
Comply with safety precautions and take
protective measures when handling
batteries. WARNING
Fire, open flames and smoking are
prohibited when handling the
battery. Avoid creating sparks.
Battery acid is caustic. Avoid
contact with the skin, eyes or
clothing.
Wear suitable protective clothing,
in particular gloves, an apron and
a face mask.
Immediately rinse acid splashes
off with clean water. Consult a
doctor if necessary.
Wear eye protection. Keep children away.
Observe this Operator's Manual.
For safety reasons, Mercedes-Benz
recommends that you only use batteries
which have been tested and approved for
your vehicle by Mercedes-Benz. These
batteries provide increased impact
protection to prevent

vehicle occupants from
suffering acid burns should the battery be
damaged in the event of an accident.
In order for the battery to achieve the
maximum possible service life, it must always
be sufficiently charged.
Like other batteries, the vehicle battery may
discharge over time if you do not use the
vehicle. In this case, have the battery
disconnected at a qualified specialist
workshop. You can also charge the battery
with a charger recommended by Mercedes-
Benz. Contact a qualified specialist workshop
for further information.
Have the battery charge level checked more
frequently if you use the vehicle mainly for
short trips or if you leave it standing idle for
a lengthy period. Consult a qualified specialist
workshop if you wish to leave your vehicle
parked for a long period of time.
Only replace a battery with a battery that has
been recommended by Mercedes-Benz.
i Remove the SmartKey if you park the
vehicle and do not require any electrical
consumers. The vehicle will then use very
little energy, thus conserving battery
power. Battery (vehicle)
287
Breakdown assistance Z
ProCarManuals.com

shorter. The starting characteristics can be impaired, particularly at low temperatures. Have
the thawed-out battery checked at a qualified specialist workshop.
Do not
start
the vehicle using a rapid charging device. If your vehicle's battery is discharged,
the engine can be jump-started from another vehicle or from a second battery using jumper
cables. Observe the following points:
R The battery is not accessible in all vehicles. If the other vehicle's battery is not accessible,
jump-start the vehicle using a second battery or a jump-starting device.
R You may only jump-start the vehicle when the engine and exhaust system are cold.
R Do not start the engine if the battery is frozen. Let the battery thaw first.
R Jump-starting may only be performed from batteries with a nominal voltage of 12 V.
R Only use jumper cables which have a sufficient cross-section and insulated terminal clamps.
R If the battery is fully discharged, leave the battery that is being used to jump-start connected
for a few minutes before attempting to start. This charges the battery slightly.
R Make sure that the two vehicles do not touch.
Make sure that:
R the jumper cables are not damaged.
R bare parts of the terminal clamp do not come into contact with other metal parts while the
jumper cables are connected to the battery.
R the jumper cables cannot come into contact with parts which can move when the engine
is running, such as the V-belt pulley or the fan.
X Secure the vehicle by applying the electric parking brake.
X Shift the transmission to position P.
X Turn the SmartKey to position 0 in the ignition lock and remove it.
X Switch off all electrical consumers (e.g. radio, blower, etc.).
X Open the hood (Y page 266).290
Jump-starting
Breakdown assistance
ProCarManuals.com

!
Only secure the
tow rope or tow bar at the
towing eyes. Otherwise, the vehicle could
be damaged.
! Do not use the towing eyes for recovery
purposes as this could damage the vehicle.
If in doubt, recover the vehicle with a crane.
! When towing, pull away slowly and
smoothly. If the tractive power is too high,
the vehicles could be damaged.
! The vehicle can be towed a maximum of
30 miles (50km). The towing speed of
30 mph (50km/h) must not be exceeded.
If the vehicle has to be towed more than
30 miles (50km), the front axle must be
raised or the entire vehicle raised and
transported.
! Do not tow with sling-type equipment.
This could damage the vehicle.
! Vehicles with automatic transmission
must not be started by tow-starting. This
could otherwise damage the transmission.
It is better to have the vehicle transported
than to have it towed.
When towing a vehicle, the transmission must
be in position N.
The battery must be connected and charged.
Otherwise, you:
R cannot turn the SmartKey to position 2 in
the ignition lock
R cannot shift the transmission to position
N.
i Deactivate the automatic locking feature
(Y page 198). You could otherwise be
locked out when pushing or towing the
vehicle. Installing/removing the towing eye
Installing the towing eye X
Remove the towing eye from the stowage
space.
The towing eye is beneath the cargo
compartment floor with

the vehicle tool kit
(Y page 280).
Vehicles with the TIREFIT kit: the towing
eye is beneath the tire inflation
compressor.
X Press the mark on cover : inwards in the
direction of the arrow.
X Take cover : off the opening.
X Screw in and tighten the towing eye
clockwise to the stop.
Removing the towing eye X
Unscrew and remove the towing eye.
X Attach cover : to the bumper and press
until it engages.
X Place the towing eye in the stowage well
beneath the cargo compartment floor
(Y page 280) in the cargo compartment.
X Vehicles with the TIREFIT kit: put back the
tire inflation compressor.292
Towing and tow-starting
Breakdown assistance
ProCarManuals.com

Towing the vehicle with the front axle
raised
! The ignition must be switched off if the
vehicle is being towed with the front axle
raised. Otherwise, ESP®

may intervene and
damage the brake system.
X Turn the SmartKey to position 2 in the
ignition lock.
X When the vehicle is stationary, depress the
brake pedal and keep it depressed.
X Shift the automatic transmission to
position P.
X Release the brake pedal.
X Release the electric parking brake.
X Deactivate automatic locking
(Y page 198).
X Switch on the hazard warning lamps
(Y page 101).
X Turn the SmartKey to position 0 in the
ignition lock and

leave the SmartKey in the
ignition lock.
When towing your vehicle with the front axle
raised, it is important that you observe the
safety instructions ( Y page 291).Towing a vehicle with both axles on
the ground
G
WARNING
The power assistance for the steering and the
brake force booster do not work when the
engine is not running. You will then need
much more effort to brake and steer the
vehicle. Adapt your style of driving
accordingly.
i In order to signal a change of direction
when towing with

the hazard warning lamps
switched on, use the combination switch as
usual. In this case, only the turn signals for
the desired direction flash. When you reset
the combination switch, the hazard
warning lamps start flashing again. The automatic transmission automatically
shifts
to position P

when you open the driver's
or front-passenger door or when you remove
the SmartKey from the ignition lock. In order
to ensure that the automatic transmission
stays in position N when towing the vehicle,
you must observe the following points:
X Make sure that the vehicle is stationary.
X Turn the SmartKey to position 2 in the
ignition lock.
X Depress and hold the brake pedal.
X Shift the automatic transmission to
position N.
X Leave the SmartKey in position 2 in the
ignition lock.
X Release the brake pedal.
X Release the electric parking brake.
X Switch on the hazard warning lamps
(Y page 101).
It is important that you observe the safety
instructions when towing away your vehicle
(Y page 291). Transporting the vehicle
! Only lash the

vehicle down by the wheels
or wheel rims, not by parts of the vehicle
such as axle or steering components.
Otherwise, the vehicle could be damaged.
X Turn the SmartKey to position 2 in the
ignition lock.
X Shift the transmission to position N.
As soon as the vehicle is loaded:
X Prevent the vehicle from rolling away by
applying the electric parking brake.
X Shift the transmission to position P.
X Turn the SmartKey to position 0 in the
ignition lock and remove it.
X Secure the vehicle.
The towing eye can be used to pull the vehicle
onto a trailer or transporter for transporting
purposes. Towing and tow-starting
293
Breakdown assistance Z
ProCarManuals.com

Tow-starting (emergency engine
starting)
! Vehicles with automatic transmission
must not be tow-started. You could
otherwise damage the automatic
transmission.
When tow-starting, it is important that you
observe the safety
instructions (Y page 291).Fuses
Important safety notes
G
WARNING
If you manipulate or bridge a faulty fuse or if
you replace it with a fuse with a higher
amperage, the electric cables could be
overloaded. This could result in a fire. There
is a risk of an accident and injury.
Always replace faulty

fuses with the specified
new fuses having the correct amperage.
! Only use fuses that have been approved
for Mercedes-Benz vehicles and which
have the correct fuse rating for the system
concerned. Only use fuses marked with an
"S". Otherwise, components or systems
could be damaged.
The fuses in your vehicle serve to close down
faulty circuits. If a fuse blows, all the
components on the circuit and their functions
stop operating.
Blown fuses must be replaced with fuses of
the same rating, which you can recognize by
the color and value. The fuse ratings are listed
in the fuse allocation chart.
If a newly inserted fuse also blows, have the
cause traced and rectified at a qualified
specialist workshop, e.g. an authorized
Mercedes-Benz Center. Before changing a fuse
X Secure the vehicle against rolling away
(Y page 149).
X Switch off all electrical consumers.
X Turn the SmartKey to position 0 in the
ignition lock and remove it (Y page 135).
All indicator lamps

in the instrument cluster
must be off.
The fuses are located in various fuse boxes:
R Fuse box in

the engine compartment on the
left-hand side of the vehicle, when viewed
in the direction of travel
R Fuse box in the front-passenger footwell
The fuse allocation chart is on the fuse box in
the front-passenger footwell ( Y page 295). Fuse box in the engine compartment
G
WARNING
When the hood is open and the windshield
wipers are set in motion, you can be injured
by the wiper linkage. There is a risk of injury.
Always switch off the windshield wipers and
the ignition before opening the hood.
! Make sure that

no moisture can enter the
fuse box when the cover is open.
! When closing the cover, make sure that it
is lying correctly on the fuse box. Moisture
seeping in or dirt could otherwise impair
the operation of the fuses. 294
Fuses
Breakdown assistance
ProCarManuals.com

Checking tire pressures manually
To determine and set the correct tire
pressure, proceed as follows:
X
Remove the valve cap of the tire that is to
be checked.
X Press the tire pressure gauge securely onto
the valve.
X Read the tire pressure and compare it with
the recommended value on the Tire and
Loading Information placard on the
B-pillar on the
driver's side of your vehicle.
X If necessary, increase the tire pressure to
the recommended value ( Y page 301).
X If the tire pressure is too high, release air
by pressing down

the metal pin in the valve
using the tip of a pen, for example. Then,
check the tire pressure again using the tire
pressure gauge.
X Screw the valve cap onto the valve.
X Repeat these steps for the other tires. Tire pressure loss warning system
Important safety notes While the vehicle is in motion, the tire
pressure loss warning system monitors the
set
tire
pressure

using the rotational speed of
the wheels. This enables the system to detect
significant pressure loss in a tire. If the speed
of rotation of a wheel changes as a result of
a loss of pressure, a corresponding warning
message will appear in the multifunction
display.
The tire pressure warning system does not
warn you of an incorrectly set tire pressure.
Observe the notes on the recommended tire
pressure ( Y page 301).
The tire pressure loss warning system does
not replace the need to regularly check your
vehicle's tire pressures, since an even loss of
pressure on several tires at the same time
cannot be detected by the tire pressure loss
warning system. The tire pressure loss warning system is not
able to
warn

you of a sudden loss of pressure,
e.g. if the tire is penetrated by a foreign
object. In the event of a sudden loss of
pressure, bring the vehicle to a halt by braking
carefully. Avoid abrupt steering maneuvers.
The function of the tire pressure loss warning
system is limited or delayed if:
R snow chains are mounted to your vehicle's
tires.
R road conditions are wintry.
R you are driving on sand or gravel.
R you adopt a very sporty driving style
(cornering at high speeds or driving with
high rates of acceleration).
R you are driving with a heavy load (in the
vehicle or on the roof).
Restarting the tire pressure loss
warning system Restart the tire pressure loss warning system
if you have:
R
changed the tire pressure
R changed the wheels or tires
R mounted new wheels or tires
X Before restarting, make sure that the tire
pressures are set properly on all four tires
for the respective operating conditions.
The recommended tire pressures can be
found in the table on the fuel filler flap.
The tire pressure loss warning system can
only give reliable warnings if you have set
the correct tire

pressure. If an incorrect tire
pressure is set, these incorrect values will
be monitored.
X Observe the notes on tire pressure
(Y page 301).
X Make sure that the SmartKey is in
position 2 (Y page 135)

in the ignition lock. Tire pressure
305
Wheels and tires Z
ProCarManuals.com

Aspect ratio
Relationship between tire height and tire
width in percent. Tire pressure
This is pressure inside the tire applying an
outward force to
each square inch of the tire's
surface. The tire pressure is specified in
pounds per square inch (psi), in kilopascal
(kPa) or in bar. The tire pressure should only
be corrected when the tires are cold. Tire pressure of cold tires
The tires are cold:
R if the vehicle has been parked without
direct sunlight on

the tires for at least three
hours and
R if the vehicle has not been driven further
than 1 mile (1.6 km) Tread
The part of the tire that comes into contact
with the road. Bead
The tire bead ensures that the tire sits
securely on the

wheel. There are several steel
wires in the bead to prevent the tire from
coming loose from the wheel rim. Sidewall
The part of

the tire between the tread and the
bead. Weight of optional extras
The combined weight

of those optional extras
that weigh more than the replaced standard
part and more than 2.3 kg (5 lbs). These optional extras, such as high-performance
brakes, level control, a roof rack or a high-
performance battery, are not included in the
curb weight and the weight of the
accessories.
TIN (Tire Identification Number)
This is a unique identifier which can be used
by a tire manufacturer to identify tires, for
example for a

product recall, and thus identify
the purchasers. The TIN is made up of the
manufacturer's identity code, tire size, tire
type code and the manufacturing date. Load bearing index
The load bearing index (also load index) is a
code that contains

the maximum load bearing
capacity of a tire. Traction
Traction is the result of friction between the
tires and the road surface. Treadwear indicators
Narrow bars (tread wear bars) that are
distributed over the

tire tread. If the tire tread
is level with the bars, the wear limit of á in
(1.6 mm) has been reached. Occupant distribution
The distribution of occupants in a vehicle at
their designated seating positions. Total load limit
Nominal load and luggage load plus
68 kilograms (150 lb) multiplied by the
number of seats in the vehicle. 318
Definition of terms for tires and loading
Wheels and tires
ProCarManuals.com

X
Switch off the engine.
X Remove the SmartKey from the ignition
lock.
X If included in the vehicle equipment,
remove the tire-change tool kit from the
vehicle.
X Secure the vehicle to prevent it from rolling
away.
Securing the vehicle to prevent it from
rolling away If your vehicle is equipped with a wheel chock,
it can be found in the tire-change tool kit
(Y page 280).
The folding wheel chock is an additional
safety measure to prevent the vehicle from
rolling away, for example when changing a
wheel.
X
Fold both plates upwards :.
X Fold out lower plate ;.
X Guide the lugs on the lower plate fully into
the openings in base plate =.Securing the vehicle on level ground X
On level ground: place chocks or other
suitable items under the front and rear of
the wheel that is diagonally opposite the
wheel you wish to change. Securing the vehicle on slight downhill gradients
X
On light downhill gradients: place
chocks or other suitable items in front of
the wheels of the front and rear axle.
Raising the vehicle G
WARNING
If you do not position the jack correctly at the
appropriate jacking point of the vehicle, the
jack could tip over with the vehicle raised.
There is a risk of injury.
Only position the jack at the appropriate
jacking point of the vehicle. The base of the
jack must be positioned vertically, directly
under the jacking point of the vehicle.
The following must be observed when
raising the vehicle:
R to raise the vehicle, only use the vehicle-
specific jack that has been tested and
approved by Mercedes-Benz. If used
incorrectly, the jack
could tip over with the
vehicle raised.
R the jack is designed only to raise and hold
the vehicle for a short time while a wheel
is being changed. It is not suited for
performing maintenance work under the
vehicle.
R avoid changing the wheel on uphill and
downhill slopes.320
Changing a wheel
Wheels and tires
ProCarManuals.com

R
before raising the vehicle, secure it from
rolling away by applying the parking brake
and inserting wheel chocks. Never
disengage the parking brake while the
vehicle is raised.
R the jack must be placed on a firm, flat and
non-slip surface. On a loose surface, a
large, load-bearing underlay
must be used.
On a slippery surface, a non-slip underlay
must be used, e.g. rubber mats.
R do not use wooden blocks or similar
objects as a jack underlay. Otherwise, the
jack will not be able to achieve its load-
bearing capacity due to the restricted
height.
R make sure that the distance between the
underside of the tires and the ground does
not exceed 1.2 inches (3 cm).
R never place your hands and feet under the
raised vehicle.
R never lie under the raised vehicle.
R never start the engine when the vehicle is
raised.
R never open or close a door or the trunk lid
when the vehicle is raised.
R make sure that no persons are present in
the vehicle when the vehicle is raised.
! The jack is designed exclusively for
jacking up the vehicle at the jacking points.
Otherwise, your vehicle could be damaged. X
Using lug wrench :, loosen the bolts on
the wheel you

wish to change by about one
full turn. Do not unscrew the bolts
completely. The jacking points are located just behind the
wheel housings of the front wheels and just
in front of the wheel housings of the rear
wheels (arrows).
X
Take the ratchet wrench out of the tire-
changing tool kit and place it on the
hexagon nut of the jack so that the letters
AUF are visible. X
Position jack = at jacking point ;. X
Make sure the foot of the jack is directly
beneath the jacking point. Changing a wheel
321
Wheels and tires Z
ProCarManuals.com