2012 MERCEDES-BENZ A CLASS check engine light

Problem Possible causes/consequences and
M SolutionsThe engine cannot be
started using the key. The on-board voltage is too low.
X
Switch off non-essential consumers, e.g. seat heating or interior
lighting, and try to start the engine again.
If this does not work:
X Check the starter battery and charge it if necessary
(Y page 304).
or
X Jump-start the vehicle (Y page 308).
or
X Consult a qualified specialist workshop. The engine cannot be
started using the key. The steering lock is mechanically blocked.
X
Remove the key and reinsert it into the ignition lock. While doing
this, turn the steering wheel in both directions. Doors
Important safety notes
G
WARNING
If children are left unsupervised in the vehicle,
they could:
R open the doors, thus endangering other
people or road users.
R get out and disrupt traffic.
R operate the vehicle's equipment.
Additionally, children could set the vehicle in
motion if, for example, they:
R release the parking brake.
R shift the automatic transmission out of
parking position P.
R shift the manual transmission into neutral.
R start the engine.
There is a risk of an accident and injury.
When
leaving the vehicle, always take the key
with you and lock the vehicle. Never leave
children or animals unattended in the vehicle.
Always keep the key out of reach of children. G
WARNING
If persons (particularly children) are exposed
to heat or cold for a prolonged period, there
is

a risk of serious or even fatal injuries. Never
leave persons (particularly children) unatten-
ded in the vehicle.
United Kingdom only: G
WARNING
When the double locks are activated, the
doors can no longer be opened from the
inside.

People in the vehicle can no longer get
out, e.g. in hazardous situations. There is a
risk of injury.
Therefore, do not leave any people unsuper-
vised in the vehicle, particularly children, eld-
erly people or people in need of special assis-
tance. Do not activate the double lock when
people are in the vehicle.
If the vehicle has been locked with the key,
then the double lock function is activated as
standard. You can deactivate the double lock
function by deactivating the interior motion
sensor (Y page 70). The doors can then be
opened from the inside after the vehicle has
been locked from the outside. The anti-theft Doors
79
Opening and closing Z

The interior lighting is activated for a short
time when the key is removed from the igni-
tion lock. You can activate this delayed
switch-off using the on-board computer
(Y page 223).
Manual interior lighting control
X
To switch the front interior lighting on:
set the switch to the c position.
X To switch off the interior lighting: set the
switch to the | position or (if the door
is closed) to the centre position.
X To switch the rear interior lighting on/
off: press the u button.
X To switch the reading lamps on/off:
press the p button. Crash-responsive emergency lighting
The
interior lighting is activated automatically
if the vehicle is involved in an accident.
X To switch off the crash-responsive
emergency lighting: press the hazard
warning lamp button.
or
X Lock and then unlock the vehicle using the
key. Replacing bulbs
Important safety notes
Xenon bulbs G
DANGER
Xenon bulbs are under high voltage. You can
get
an electric shock if you remove the cover
of the xenon bulb and touch the electrical
contacts. There is a risk of fatal injury.
Never touch the parts or the electrical con-
tacts of the xenon bulb. Always have work on
the xenon bulbs carried out at a qualified spe-
cialist workshop. If your vehicle is equipped with xenon bulbs,
you can recognise this by the following: the
cone of light from the xenon bulbs moves
from the top to the bottom and back again
when you start the engine. For this to be
observed, the lights must be switched on
before starting the engine.
Bulbs and lamps are an important aspect of
vehicle

safety. You must therefore make sure
that these function correctly at all times.
Have the headlamp setting checked regularly.
Other bulbs G
WARNING
Bulbs, lamps and plug connectors can
become very hot during use. When replacing
a

bulb, you could burn yourself on these com-
ponents. There is a risk of injury.
Allow these components to cool down before
replacing the bulb.
There are bulbs other than the xenon bulbs
that you cannot replace. Replace only the
bulbs listed (Y page 113). Have the bulbs that
you cannot replace yourself replaced at a
qualified specialist workshop.
If you require assistance replacing bulbs, con-
sult a qualified specialist workshop.
Do not touch the glass tube of new bulbs with
your bare hands. Even minor contamination
can burn into the glass surface and reduce
the service life of the bulbs. Always use a lint-
free cloth or only touch the base of the bulb
when fitting.
Only use bulbs of the correct type.
If the new bulb still does not light up, consult
a qualified specialist workshop.
Bulbs and lamps are an important aspect of
vehicle safety. You must therefore make sure
that these function correctly at all times.
Have the headlamp setting checked regularly. 112
Replacing bulbs
Lights and windscreen wipers

Problem Possible causes/consequences and
M SolutionsVehicles with a petrol
engine:
The engine is not run-
ning smoothly and is
misfiring. There is a malfunction in the engine electronics or in a mechanical
component of the engine management system.
X
Only depress the accelerator pedal slightly.
Otherwise, non-combusted fuel may get into the catalytic con-
verter and damage it.
X Have the cause rectified immediately at a qualified specialist
workshop. The coolant tempera-
ture display is showing
more than 120
†. The
coolant warning lamp
may also be on and a
warning tone may
sound. The coolant level is too low. The coolant is too hot and the engine
is no longer being cooled sufficiently.
X
Stop as soon as possible and allow the engine and the coolant
to cool down.
X Check the coolant level (Y page 288). Observe the warning
notes as you do so and top up the coolant if necessary. If the coolant level is correct, the engine radiator fan may be faulty.
The coolant is too hot and the engine is no longer being cooled
sufficiently.
X
If the coolant temperature is below 120 †, you can continue
driving to the nearest qualified specialist workshop.
X Avoid heavy loads on the engine as you do so, e.g. driving in
mountainous terrain and stop-start traffic. Manual transmission
Gear lever
! Only engage gear when the clutch pedal
is depressed.
! When shifting to 5th and 6th gear, you
must

press the shift lever to the right. Oth-
erwise, you could shift unintentionally into
3rd or 4th gear and damage the engine or
transmission.
If you shift down at too high a speed (trans-
mission braking), this can cause the engine
to overrev, leading to engine damage.
Do not use the clutch bite point to keep the
vehicle stationary on uphill gradients.
There is otherwise a risk of damaging the
clutch.
! On long and steep downhill gradients,
especially if the vehicle is laden or towing a trailer, you must shift into gear
1, 2 or 3
in
good time. This uses the engine's braking
effect. This relieves the load on the brake
system and prevents the brakes from over-
heating and wearing too quickly. Gear lever
k
Reverse gear
1 to 6 Forward gears150
Manual transmission
Driving and parking

cle from rolling away by applying the parking
brake.
Vehicles with manual transmission X
Shift to either first gear or reverse gear R.
X Turn the key to position 0 in the ignition
lock and remove it.
The immobiliser is activated.
X Apply the electric parking brake.
Vehicles with automatic transmission All vehicles (except AMG vehicles)
X
Apply the electric parking brake.
X Shift the transmission to position P.Selector lever in AMG vehicles
AMG vehicles:
X
Apply the electric parking brake.
X Press P button :.
X Turn the key to position 0 in the ignition
lock and remove it.
The immobiliser is activated.
i If you switch the engine off with the trans-
mission in position R or D, the automatic
transmission shifts to N automatically.
If you then open one of the front doors or
remove the key from the ignition, the auto-
matic transmission shifts to P.
If you shift the automatic transmission to
N before switching off the engine, the auto-
matic transmission remains in N even if a
door is opened. Electric parking brake
General notes G
WARNING
If you leave children unattended in the vehi-
cle, they could set the vehicle in motion by,
for example:
R releasing the parking brake
R shifting an automatic transmission out of
parking position P
R shifting

a manual transmission into neutral
R starting the engine
They could also operate vehicle equipment.
There is a risk of an accident and injury.
When leaving the vehicle, always take the key
with you and lock the vehicle. Never leave
children unattended in the vehicle. i
The electric parking brake carries out a
function check at regular intervals when
the engine is switched off. Noises that
occur are normal.
Engaging/releasing manually Engaging
X
Push handle :.
When
the electric parking brake is applied,
the ! red indicator lamp lights up in the
instrument cluster.
i The electric parking brake can also be
applied when the key is removed. Parking
163
Driving and parking Z

Cruise control lever
You can operate cruise control and variable
SPEEDTRONIC with the cruise control lever.
The LIM indicator lamp on the cruise control
lever
indicates which system you have selec-
ted:
R LIM indicator lamp off: cruise control is
selected.
R LIM indicator lamp on: variable SPEED-
TRONIC is selected. :
To activate or increase speed
; LIM indicator lamp
= To activate at the current speed/last
stored speed
? To activate or reduce speed
A To switch between cruise control and var-
iable SPEEDTRONIC
B To deactivate cruise control
When you activate cruise control, the stored
speed is shown in the multifunction display
for five seconds.
In the multifunction display, the segments
between

the stored speed and the maximum
speed light up.
Activation conditions To activate cruise control, all of the following
activation conditions must be fulfilled:
R
the electric parking brake must be
released.
R you are driving faster than 30 km/h. R
ESP ®
must be switched on, but not inter-
vening.
R on vehicles with automatic transmission,
the selector lever must be in position D.
R on vehicles with manual transmission, a
gear must be engaged.
R cruise control must be selected.
X To select cruise control: check whether
LIM indicator lamp ; is on or off.
If

it is off, cruise control is already selected.
X If it is not, press the cruise control lever in
the direction of arrow A.
LIM

indicator lamp ; in the cruise control
lever goes out. Cruise control is selected.
Storing, maintaining and calling up a
speed Storing and maintaining the current
speed
You can store the current speed if you are
driving faster than 30 km/h

.
X Accelerate the vehicle to the desired
speed.
X Briefly press the cruise control lever
up : or down ?.
X Remove your foot from the accelerator
pedal.
Cruise control is activated. The vehicle
automatically maintains the speed.
i Cruise
control may be unable to maintain
the stored speed on uphill gradients. The
stored speed is resumed when the gradient
evens out. Cruise control maintains the
stored speed on downhill gradients by
automatically braking the vehicle.
i Vehicles with manual transmission:
R always drive at adequate, but not exces-
sive, engine speeds.
R change gear in good time.
R if possible, do not change down several
gears at a time. Driving systems
169
Driving and parking Z

SPEEDTRONIC
Important safety notes SPEEDTRONIC brakes automatically so that
you
do not exceed the set speed. On long and
steep downhill gradients, especially if the
vehicle is laden or towing a trailer, you must
select shift range 1, 2 or 3 in good time. By
doing so, you will make use of the braking
effect of the engine. This relieves the load on
the brake system and prevents the brakes
from overheating and wearing too quickly. If
you need additional braking, depress the
brake pedal repeatedly rather than continu-
ously.
If you fail to adapt your driving style, SPEED-
TRONIC can neither reduce the risk of an
accident nor override the laws of physics.
SPEEDTRONIC cannot take into account
road, weather or traffic conditions. SPEED-
TRONIC is only an aid. You are responsible for
the distance to the vehicle in front, for vehicle
speed, for braking in good time, and for stay-
ing in the lane.
If there is a change of drivers, advise the new
driver of the speed stored.
General notes You can set a variable or permanent limit
speed:
R
variable for speed limits, e.g. in built-up
areas
R permanent for long-term speed restric-
tions, e.g. when driving with winter tyres
fitted (Y page 172)
i The speed indicated in the speedometer
may differ slightly from the limit speed
stored.
Variable SPEEDTRONIC General notes
With

the cruise control lever, you can operate
cruise control or DISTRONIC PLUS and vari-
able SPEEDTRONIC. The LIM indicator lamp on the cruise control
lever

indicates which system you have selec-
ted:
R LIM indicator lamp off: cruise control or
DISTRONIC PLUS is selected.
R LIM indicator lamp on: variable SPEED-
TRONIC is selected.
You can use the cruise control lever to limit
the speed to any speed above 30 km/h while
the engine is running. :
To store the current speed or a higher
speed
; LIM indicator lamp
= To store the current speed and calling up
the last stored speed
? To store the current speed or a lower
speed
A To switch between cruise control or DIS-
TRONIC

PLUS and variable SPEEDTRONIC
B To deactivate variable SPEEDTRONIC
Selecting variable SPEEDTRONIC
X Check whether LIM indicator lamp ;
is on.
If it is on, variable SPEEDTRONIC is already
selected.
If it is not, press the cruise control lever in
the direction of arrow A.
LIM indicator lamp ; in the cruise control
lever lights up. Variable SPEEDTRONIC is
selected.
X Make sure that the accelerator pedal is not
depressed beyond the pressure point. Driving systems
171
Driving and parking Z

Indicator and warning display
Blind
Spot Assist is not active at speeds below
approximately 30 km/h. Vehicles in the mon-
itoring range are then not indicated. :
Yellow indicator lamp/red warning lamp
If Blind Spot Assist is switched on, indicator
lamp : in the exterior mirrors lights up yel-
low up to a speed of

30 km/h. At speeds
above 30 km/h, the indicator lamp goes out
and Blind Spot Assist is operational.
If a vehicle is detected within the monitoring
range of Blind Spot Assist at speeds above
30 km/h, warning lamp : on the corre-
sponding side lights up in red. This warning
always occurs when a vehicle enters the blind
spot monitoring range from behind or from
the side. When you overtake a vehicle, the
warning only occurs if the difference in speed
is less than 12 km/h.
The yellow indicator lamp goes out if reverse
gear is engaged. Blind Spot Assist is then
deactivated.
The brightness of the indicator/warning
lamps is adjusted automatically according to
the ambient light.
Collision warning
If a vehicle is detected in the monitoring range
of Blind Spot Assist and you switch on the
corresponding turn signal, a double warning
tone sounds. Red warning lamp : flashes. If
the turn signal remains on, detected vehicles
are indicated by the flashing of red warning
lamp :. There are no further warning tones. Activating Blind Spot Assist
X
Make sure that the radar sensor system
(Y page 223) and Blind Spot Assist
(Y page

219) are activated in the on-board
computer.
X Turn the key to position 2 in the ignition
lock.
Warning lamps : in the exterior mirrors
light up red for approximately
1.5 seconds

and then turn yellow.
Towing a trailer
If
you attach a trailer, make sure that you have
correctly established the electrical connec-
tion. This can be accomplished by checking
the trailer lighting. Blind Spot Assist is then
deactivated. The indicator lamp lights up yel-
low in the exterior mirrors and the Blind
Spot Assist currently unavailable
See Owner's Manual message appears in
the multifunction display.
i You can deactivate the indicator lamps in
the exterior mirrors.
To do so, switch off Blind Spot Assist if:
R the key is in position 2 in the ignition
lock.
R the engine is not running.
R the electrical connection to the trailer
has been established.
Lane Keeping Assist General notes
Lane Keeping Assist monitors the area in
front

of your vehicle by means of a camera at
the top of the windscreen. Lane Keeping
Assist detects lane markings on the road and
warns you before you leave your lane unin-
tentionally. Driving systems
199
Driving and parking Z

Useful information
i This Owner's Manual describes all mod-
els,
series and optional equipment for your
vehicle that were available at the time of
going to press. National variations are pos-
sible. Note that your vehicle may not be
equipped with all of the functions descri-
bed. This is also the case for systems and
functions relevant to safety.
i Read the information on qualified special-
ist workshops: (Y page 24). Important safety notes
G
WARNING
Operating the integrated information systems
and
communications equipment in the vehicle
while driving will distract you from traffic con-
ditions. You could then lose control of the
vehicle. There is a risk of an accident.
Only operate these devices if road traffic con-
ditions permit. If you are unsure about the
surrounding conditions, pull over to a safe
location and make entries only while the vehi-
cle is stationary. G
WARNING
If the instrument cluster has failed or mal-
functioned, you may not recognise function
restrictions 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 immedi-
ately.
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 mul-
tifunction display. You should therefore make
sure your vehicle is operating safely at all times. Otherwise, a vehicle that is not oper-
ating safely may cause an accident.
For an overview, see the instrument panel
illustration (
Y page 30). Displays and operation
Instrument cluster lighting
The lighting in the instrument cluster, in the
displays and the controls in the vehicle inte-
rior

can be adjusted using the brightness con-
trol knob.
The brightness control knob is on the bottom
left of the instrument cluster ( Y page 30).
X Turn the brightness control knob clockwise
or anti-clockwise.
If the light switch is set to Ã, T or
L, the brightness is dependant 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 gauge
The coolant temperature gauge is in the
instrument cluster on the right-hand side.
The

reading may rise up to 120 † below nor-
mal driving conditions if the coolant has been
filled correctly.
At high outside temperatures and when driv-
ing uphill, the coolant temperature may rise
to the end of the scale. Rev counter
! Do not drive in the overrevving range.
Doing so will damage the engine.
The

red band in the rev counter indicates the
engine's overrevving range. 208
Displays and operation
On-board computer and displays