check engine light MERCEDES-BENZ B-CLASS 2012 User Guide

brake pads. This can result in a significantly
longer braking distance.
R
Brake occasionally to
remove any possible
salt residue. Make sure that you do not
endanger other road users when doing so.
R Carefully depress the brake pedal and the
beginning and end of a journey.
R Maintain a greater distance to the vehicle
ahead.
Servicing the brakes !
If the red

brake warning lamp lights up in
the instrument cluster and you hear a
warning tone while the engine is running,
the brake fluid level may be too low.
Observe additional warning messages in
the multifunction display.
The brake fluid level may be too low due to
brake pad wear or leaking brake lines.
Have the brake system checked
immediately. This work should be carried
out at a qualified specialist workshop.
! A function or performance test should
only be carried out on a 2-axle
dynamometer. If you are planning to have
the vehicle tested on such a dynamometer,
contact an authorized Mercedes-Benz
Center to obtain further information first.
Otherwise, you could damage the drive
train or the brake system.
! As the ESP ®
system operates
automatically, the engine and the ignition
must be switched off (the SmartKey must
be in position 0 or 1 in the ignition lock) if:
R the electric parking brake is tested on a
brake dynamometer (for a maximum of
ten seconds)
R the vehicle is towed with the front axle
raised.
Braking triggered automatically by ESP ®
may seriously damage the brake system.
All checks and maintenance work on the
brake system must be carried out at a qualified specialist workshop. Consult a
qualified
specialist workshop

to arrange this.
Have brake pads installed and brake fluid
replaced at a qualified specialist workshop.
If the brake system has only been subject to
moderate loads, you should test the
functionality of your brakes at regular
intervals.
You can find a description of Brake Assist
(BAS) on ( Y page 59).
Mercedes-Benz recommends that you only
have brake pads/linings installed on your
vehicle which have been approved for
Mercedes-Benz vehicles or which correspond
to an equivalent quality standard. Brake
pads/linings which have not been approved
for Mercedes-Benz vehicles or which are not
of an equivalent quality could affect your
vehicle's operating safety.
Mercedes-Benz recommends that you only
use brake fluid that has been specially
approved for your vehicle by Mercedes-Benz,
or which corresponds to an equivalent quality
standard. Brake fluid which has not been
approved for Mercedes-Benz vehicles or
which is not of an equivalent quality could
affect your vehicle's operating safety.
Checking brake lining thickness You can measure the break pad/lining
thickness using a test gauge. Color-coding
(green or
red)

on the test gauge allows you to
determine whether the brake pad/lining
thickness is still sufficient. The test gauge is
in the vehicle document wallet in the glove
box. Driving tips
155
Driving and parking Z
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Useful information
i This Operator's Manual describes all
models and all standard and optional
equipment of your vehicle available at the
time of publication of the Operator's
Manual. Country-specific differences are
possible. Please note
that your vehicle may
not be equipped with all features
described. This also applies to safety-
related systems and functions.
i Read the information on qualified
specialist workshops: ( Y page 24).Important safety notes
G
WARNING
If you operate information systems and
communication equipment integrated in the
vehicle while driving, you will be distracted
from traffic conditions. You could also lose
control of the vehicle. There is a risk of an
accident.
Only operate the equipment when the traffic
situation permits. If

you are not sure that this
is possible, park the vehicle paying attention
to traffic conditions and operate the
equipment when the vehicle is stationary. G
WARNING
If the instrument cluster has failed or
malfunctioned, you may not recognize
function restrictions in systems relevant to
safety. The operating safety of your vehicle
may be impaired. There is a risk of an
accident.
Drive on carefully. Have the vehicle checked
at a qualified specialist workshop
immediately.
You must observe the legal requirements for
the country in

which you are currently driving
when operating the on-board computer.
The on-board computer only shows messages
or warnings from certain systems in the multifunction display. You should therefore
make sure your vehicle is operating safely at
all times. Otherwise, a vehicle that is not
operating safely may cause an accident.
For an overview, see the instrument panel
illustration (
Y page 29). Displays and operation
Instrument cluster lighting
The lighting in the instrument cluster, in the
displays and the controls in the vehicle
interior can be

adjusted using the brightness
control knob.
The brightness control knob is located on the
bottom left of the instrument cluster
(Y page 29).
X Turn the brightness control knob clockwise
or counter-clockwise.
If the light switch is set to Ã, T or
L, the brightness is dependent upon
the brightness of the ambient light.
i The light sensor

in the instrument cluster
automatically controls the brightness of
the multifunction display.
In daylight, the displays in the instrument
cluster are not illuminated. Coolant temperature display
G
WARNING
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.
Stop the vehicle in a safe location away from
other traffic. Turn off the engine, get out of the
vehicle and do not stand near the vehicle until
the engine has cooled down. 186
Displays and operation
On-board computer and displays
ProCarManuals.com

Display messages Possible causes/consequences and
M Solutionsb
Switch Off Lights The lights are still switched on when you leave the vehicle. A
warning tone also sounds.
X
Turn the light switch to Ã. Adaptive Highbeam
Assist Inoperative Adaptive Highbeam Assist is faulty.
X
Visit a qualified specialist workshop. Adaptive Highbeam
Assist Currently
Unavailable See
Operator's Manual Adaptive Highbeam Assist is deactivated and temporarily
inoperative. Possible causes are:
R
the windshield in the camera's field of vision is dirty.
R visibility is impaired due to heavy rain, snow or fog.
X Clean the windshield.
If the system detects that the camera is fully operational again,
the Adaptive Highbeam Assist Now Available message is
displayed.
Adaptive Highbeam Assist is operational again. Engine
Display messages Possible causes/consequences and
M Solutions+
Check Coolant
Level See
Operator's Manual The coolant level is too low.
!
Avoid making long
journeys with too little coolant in the engine
cooling system. The engine will otherwise be damaged.
X Add coolant, observing the warning notes before doing so
(Y page 269).
X If coolant needs to be added more often than usual, have the
engine coolant system checked at a qualified specialist
workshop. ? The fan motor is faulty.
X
At coolant temperatures below 248 ‡ (120 †), drive to the
nearest qualified specialist workshop.
X Avoid subjecting the engine to heavy loads, e.g. driving in
mountainous terrain, and stop-and-go traffic.212
Display messages
On-board computer and displays
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Problem Possible causes/consequences and
M SolutionsF (USA only)
! (Canada only)
The red indicator lamp
for the electric parking
brake flashes or lights
up and/or the yellow
warning lamp for the
electric parking brake
lights up. X
Observe the additional display messages in the multifunction
display. 6
The red SRS warning
lamp is lit while the
engine is running.
There is a malfunction in the SRS (Supplemental Restraint
System).
G WARNING
The air bags or Emergency Tensioning Devices may either be
triggered unintentionally or, in the event of an accident, may not
be triggered.
There is an increased risk of injury.
X Drive on carefully.
X Have SRS checked at a qualified specialist workshop
immediately.
For further information about SRS, see (Y page 38). 230
Warning and indicator lamps in the instrument clusterOn-board computer and displays
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Engine
Problem Possible causes/consequences and
M Solutions;
The yellow Check
Engine warning lamp
lights up while the
engine is running.
There may be a malfunction, for example:
R
in the engine management
R in the fuel injection system
R in the exhaust system
R in the ignition system
R in the fuel system
The emission limit values may be exceeded and the engine may
be running in emergency mode.
X Have the vehicle checked as soon as possible at a qualified
specialist workshop.
i In some states, you must immediately visit a qualified
specialist workshop as
soon as the yellow Check Engine warning
lamp lights up. This depends on the locally applicable legal
requirements. If in doubt, check whether such legal regulations
apply in the state in which you are currently driving. æ
The yellow reserve fuel
warning lamp lights up
while the engine is
running.
The fuel level has dropped into the reserve range.
X
Refuel at the nearest gas station. æ
The yellow reserve fuel
warning lamp flashes
while the engine is
running.
The fuel system pressure is too low. The fuel filler cap is not closed
correctly or the fuel system is leaking.
X
Check that the fuel filler cap is correctly closed.
X If the fuel filler cap is not correctly closed:
close the

fuel filler
cap.
X If the fuel filler cap is closed: visit a qualified specialist
workshop. ?
The red coolant
warning lamp lights up
while the engine is
running and
the

coolant
temperature gage is at
the start of the scale. The temperature sensor for the coolant temperature gage is
defective.
The coolant
temperature
is no longer being monitored. There is a
risk of engine damage if the coolant temperature is too high.
X Pull over and stop the vehicle safely and switch off the engine,
paying attention to

road and traffic conditions. Do not continue
driving under any circumstances.
X Secure the vehicle against rolling away ( Y page 149).
X Consult a qualified specialist workshop. Warning and indicator lamps in the instrument cluster
231
On-board computer and displays Z
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Problem Possible causes/consequences and
M SolutionsX
Leave the vehicle and keep a safe distance from the vehicle until
the engine has cooled down.
X Check the coolant level and add coolant (Y page 269). Observe
the warning notes.
X If you need to add coolant more often than usual, have the
engine coolant system checked.
X Make sure that the air supply to the engine radiator is not
blocked, e.g. by snow, slush or ice.
X At
coolant temperatures under 248 ‡ (120 †),
drive to the next
qualified specialist workshop.
X Avoid subjecting the engine to heavy loads, e.g. driving in
mountainous terrain, and stop-and-go traffic. Driving systems
Problem Possible causes/consequences and
M Solutions·
The red distance
warning lamp lights up
while the vehicle is in
motion. A
warning

tone
also sounds. You are approaching a vehicle or a stationary obstacle in your line
of travel at too high a speed.
X
Be prepared to brake immediately.
X Pay careful attention to the traffic situation. You may have to
brake or take evasive action. Warning and indicator lamps in the instrument cluster
233
On-board computer and displays Z
ProCarManuals.com

!
Make sure that
the windshield wipers are
not folded away from the windshield. You
could otherwise damage the windshield
wipers or the hood. X
Make sure that the windshield wipers are
switched off.
X Pull release lever : on the hood.
The hood is released. X
Reach into the gap between the hood and
the radiator trim and press hood catch
lever ; to the left.
X Raise the hood. X
Pull support strut ? out of bracket A.
X Lift up support strut ? and insert it into
yellow retaining clip =.
Closing the hood X
Raise the hood slightly and, at the same
time, remove support strut ? from yellow
retaining clip =.
X Swing support strut ? down and press it
into bracket A until it engages.
X Lower the hood and let it fall from a height
of approximately 8 in (20 cm).
X Check that

the hood has engaged properly.
If the hood can be raised slightly, it is not
properly engaged. Do not press the hood
closed. Open the hood again and close it
with a little more force. Engine oil
General notes Depending on the driving style, the vehicle
consumes up to 0.9 US qt (0.8 liters) of oil
over a

distance of 600 miles (1,000 km). The
oil consumption may be higher than this when
the vehicle is new or if you frequently drive at
high engine speeds.
Depending on the engine, the oil dipstick may
be in a different location.
When checking the oil level:
R park the vehicle on a level surface.
R the engine should be switched off for
approximately five minutes if the engine is
at normal operating temperature.
R if the engine is not at normal operating
temperature, e.g. if the engine was only
started briefly: wait about 30 minutes
before carrying out the measurement. Engine compartment
267
Maintenance and care Z
ProCarManuals.com

i
If the power supply has been interrupted,
e.g. if you reconnect the battery, you will
have to:
R set the clock (audio system/COMAND,
see the
separate operating instructions).
R reset the function for folding the exterior
mirrors in/out automatically, by folding
the mirrors out once ( Y page 93).Charging the battery
G
WARNING
During charging and jump-starting, explosive
gases can escape

from the battery. There is a
risk of an explosion.
Particularly avoid fire, open flames, creating
sparks and smoking. Ensure there is sufficient
ventilation while charging and jump-starting.
Do not lean over a battery. G
WARNING
Battery acid is caustic. There is a risk of injury.
Avoid contact with

the skin, eyes or clothing.
Do not inhale any battery gases. Do not lean
over the battery. Keep children away from
batteries. Wash battery acid immediately with
water and seek medical attention. G
WARNING
A discharged battery can freeze at
temperatures below freezing point. When
jump-starting the vehicle or charging the
battery, gases can escape from the battery.
There is a risk of an explosion.
Allow the frozen battery to thaw out before
charging it or jump-starting.
! Only use battery chargers with a
maximum charging voltage of 14.8 V.
! Only charge the battery using the jump-
starting connection point.
The jump-starting connection point is in the
engine compartment (Y

page 289). X
Open the hood (Y page 266).
X Connect the battery charger to the positive
terminal and ground point in the same
order as when connecting the donor
battery in the jump-starting procedure
(Y page 289).
If, at low temperatures, the indicator lamps/
warning lamps in the instrument cluster do
not light up, it is highly likely that the
discharged battery has frozen. In this case
you may neither jump-start the vehicle nor
charge the battery. The service life of a
thawed-out battery may be shorter. The
starting characteristics can be impaired,
particularly at low temperatures. Have the
thawed-out battery checked at a qualified
specialist workshop.
Only charge the installed battery with a
battery charger which has been tested and
approved by Mercedes-Benz. An accessory
battery charge unit specially adapted for
Mercedes-Benz vehicles and tested and
approved by Mercedes-Benz is available. It
permits the charging of the battery in its
installed position. Contact an authorized
Mercedes-Benz Center for further
information and availability.

Read the battery
charger's operating instructions before
charging the battery. 288
Battery (vehicle)
Breakdown assistance
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
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