
Display messages
Possible causes/consequences and
X
X Solutions b Malfunc‐
tion See
Owner's
Manual The exterior lighting is faulty.
X
Visit a qualified specialist workshop. Vehicles with trailer coupling*: a fuse may have blown.
X
Check the fuses (Y page 328).
X If necessary, replace the blown fuse. Observe the warning
notes.
If the display message continues to be shown:
X Visit a qualified specialist workshop. ¸ Replace
air
cleaner
The engine air filter is dirty and must be replaced
42
.
X Visit a qualified specialist workshop. 4 Check
eng. oil
lev. when
next refu‐
elling The engine oil level has dropped to a critical level. A warning
tone also sounds.
X
Check the engine oil level ( Ypage 220).
X If necessary, top up the engine oil.
X Have the engine checked for leaks if the engine oil needs
topping up more often than usual. + Change
key bat‐
teries The key batteries are discharged.
X
Change the batteries ( Ypage 304). + Key not
detected
(red display
message)
The KEYLESS GO key* is not in the vehicle. A warning tone
also sounds.
If you switch off the engine, you can no longer centrally lock
the vehicle and no longer start the engine.
X
Pull over and stop the vehicle safely as soon as possible,
paying attention to road and traffic conditions.
X Locate the KEYLESS GO key*. The KEYLESS GO key* is not detected while driving because
a powerful radio transmitter is causing interference. A warn-
ing tone also sounds.
X
Pull over and stop the vehicle safely as soon as possible,
paying attention to road and traffic conditions.
X Remove the Start/Stop button* from the ignition
lock (Y page 75).
X Insert the key into the ignition lock and turn it to the desired
position. 42
Only for certain vehicles. 274
Display
messagesPractical advice
* optional
212_AKB; 2; 4, en-GB
mkalafa
,V ersion: 2.11.8.1
2009-05-05T14:17:16+02:00 - Seite 274
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:11; WK 

Display messages
Possible causes/consequences and
X
X Solutions + Key not
detected
(white dis-
play mes-
sage) You want to unlock or lock the vehicle and the KEYLESS GO
key* cannot be currently detected by the vehicle.
X
Locate the KEYLESS GO key*.
If the KEYLESS GO key* is still not detected:
X Lock or unlock the vehicle using the key. You are in the vehicle and the KEYLESS GO key* currently
cannot be detected by the vehicle.
X
Change the location of the KEYLESS GO key* in the vehicle.
If the KEYLESS GO key* is still not detected:
X Remove the Start/Stop button* from the ignition
lock (Y page 75).
X Insert the key into the ignition lock and turn it to the desired
position. + Key still
in vehicle
The KEYLESS GO key* has been detected inside the vehicle
during locking.
X
Remove the KEYLESS GO key* from the vehicle. + Replace
key The key must be replaced.
X
Visit a qualified specialist workshop. + Key does
not
belong to
vehicle You have put the wrong key in the ignition lock.
X
Use the correct key. + Close
doors to
lock vehi‐
cle At least one door is open. A warning tone also sounds.
X
Close all doors and lock the vehicle again. + Pull
starting
button
out then
insert key
KEYLESS GO* is temporarily malfunctioning or is defective. A
warning tone also sounds.
X
Remove the Start/Stop button* from the ignition
lock (Y page 75).
X Insert the key into the ignition lock and turn it to the desired
position. Display
messages
275Practical advice
* optional
212_AKB; 2; 4, en-GB
mkalafa
,V ersion: 2.11.8.1
2009-05-05T14:17:16+02:00 - Seite 275 Z
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:11; WK 

Problem
Possible causes/consequences and
X
X Solutions Vehicles with the ECO
Start/Stop function:
you have started the
engine using the key.
The indicator lamp in
the ECO Start/Stop
function button does
not light up or goes out
again after a short time. You have deactivated the ECO Start/Stop function.
X
Activate the ECO Start/Stop function again (Y page 109). The ECO Start/Stop function is not available due to a fault.
X If the indicator lamp fails persistently, consult a qualified work-
shop. Warning and indicator lamps in the instrument cluster
Problem
Possible causes/consequences and
X
X Solutions !
The yellow ABS
warning lamp is
lit while the
engine is run-
ning. G
Risk of accident
ABS (Anti-lock Brake System) is deactivated due to a fault. For this
reason, ESP ®
(Electronic Stability Program), BAS (Brake Assist),
BAS PLUS* (Brake Assist PLUS), PRE-SAFE ®
, PRE-SAFE ®
Brake*,
the HOLD function, hill start assist and ESP ®
trailer stabilisation
are also deactivated, for example.
The brake system continues to function normally, but without the
functions listed above. Therefore, the wheels could lock if you
brake hard.
ATTENTION ASSIST is deactivated.
X Observe the additional messages in the multi-function display
(Y page 251).
X Drive on carefully.
X Visit a qualified specialist workshop. ·
The red distance
warning lamp*
lights up while
the vehicle is in
motion. G
Risk of accident
The distance to the vehicle in front is too small for the speed
selected.
X Increase the distance. ·
The red distance
warning lamp*
lights up while
the vehicle is in
motion. A warn-
ing tone also
sounds. G
Risk of accident
You are approaching a vehicle in front at too great 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. Troubleshooting
281Practical advice
* optional
212_AKB; 2; 4, en-GB
mkalafa,
Version: 2.11.8.1 2009-05-05T14:17:16+02:00 - Seite 281 Z
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:12; WK 

Problem
Possible causes/consequences and
X XSolutions J
The red brake
system warning
lamp comes on
while the vehicle
is moving. A
warning tone
also sounds. You are driving with the parking brake applied.
X
Release the parking brake.
The warning lamp goes out and the warning tone ceases. J
The red brake
system warning
lamp comes on
while the engine
is running. G
Risk of accident
The brake boosting effect is malfunctioning and the braking char-
acteristics may be affected.
X Pull over and stop the vehicle safely as soon as possible, paying
attention to road and traffic conditions. Do not continue driving
under any circumstances.
X Consult a qualified specialist workshop.
X Observe the additional messages in the multi-function display
(Y page 251). J
The red brake
system warning
lamp comes on
while the engine
is running. A
warning tone
also sounds. G
Risk of accident
There is insufficient brake fluid in the fluid reservoir.
X Pull over and stop the vehicle safely as soon as possible, paying
attention to road and traffic conditions. Do not continue driving
under any circumstances.
X Consult a qualified specialist workshop.
X Observe the additional messages in the multi-function display
(Y page 251).
Do not top up the brake fluid. This will not rectify the fault. ?
The red coolant
warning lamp
lights up while
the engine is
running and the
coolant temper-
ature gauge is at
the start of the
scale. The temperature sensor for the coolant temperature gauge is
faulty.
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 Consult a qualified specialist workshop. 284
TroubleshootingPractical advice
212_AKB; 2; 4, en-GB
mkalafa,
Version: 2.11.8.1 2009-05-05T14:17:16+02:00 - Seite 284
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:12; WK 

Problem
Possible causes/consequences and
X
X Solutions ?
The red coolant
warning lamp
comes on while
the engine is
running. A warn-
ing tone also
sounds. The coolant temperature has exceeded 130 †. The airflow to the
radiator may be blocked or the coolant level may be too low.
The engine is not being cooled sufficiently and may be damaged.
X
Pull over and stop the vehicle safely and switch off the engine,
paying attention to road and traffic conditions.
X Allow the engine and coolant to cool.
X Make sure that the air supply to the radiator is not blocked, e.g.
by slush.
X Check the coolant level (Y page 221). Observe the warning
notes.
X If necessary, top up the coolant.
X Have the engine cooling system checked at a qualified specialist
workshop if the coolant needs topping up more often than usual.
If the coolant level is correct, the electric radiator fan may be
faulty.
X Do not continue driving under any circumstances.
X Consult a qualified specialist workshop. ;
The yellow
engine diagnos-
tics warning
lamp lights up
while the engine
is running. Vehicles with a diesel engine: the fuel tank has been run dry.
X
Start the engine three to four times after refuelling.
Emergency running mode is cancelled. The vehicle need not be
checked. ;
The yellow
engine diagnos-
tics warning
lamp lights up
while the engine
is running. There may be a fault, for example:
R
in the engine management
R in the ignition system
R in the exhaust system
R in the ignition system (for vehicles with petrol engines)
The emission limit values may be exceeded and the engine can
run in emergency mode.
X Have the vehicle checked as soon as possible at a qualified
specialist workshop. Troubleshooting
285Practical advice
212_AKB; 2; 4, en-GB
mkalafa, Version: 2.11.8.1 2009-05-05T14:17:16+02:00 - Seite 285 Z
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:12; WK 

Problem
Possible causes/consequences and
X XSolutions h
The yellow tyre
pressure moni-
tor* warning
lamp is on. G
Risk of accident
The tyre pressure monitor* has detected a sudden or significant
pressure loss in at least one of the tyres.
X Stop the vehicle without making any sudden steering or braking
manoeuvres. Pay attention to traffic conditions as you do so.
X Observe the additional messages in the multi-function display
(Y page 251). 7
The red seat belt
warning lamp
lights up for six
seconds after
the engine is
started 43
. The seat belt warning lamp reminds the driver and front passenger
to fasten their seat belts.
X
Fasten your seat belt (Y page 89).7
After the engine
starts, a warning
tone sounds for
up to six sec-
onds43
. G
Risk of injury
The driver's seat belt is not fastened.
X Fasten your seat belt (Y page 89).
The warning tone ceases. 7
The red seat belt
warning lamp
lights up after
the engine
starts, as soon
as the driver's
door or the
front-passenger
door is closed. G
Risk of injury
The driver or front passenger has not fastened their seat belt.
X Fasten your seat belt (Y page 89).
The warning lamp goes out. G
Risk of injury
There are objects on the front-passenger seat.
X Remove the objects from the front-passenger seat and stow
them safely.
The warning lamp goes out. 43
Only for certain countries. 286
TroubleshootingPractical advice
* optional
212_AKB; 2; 4, en-GB
mkalafa,
Version: 2.11.8.1 2009-05-05T14:17:16+02:00 - Seite 286
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:12; WK 

Engine
Problem
Possible causes/consequences and
X
X Solutions The engine will not
start.
The HOLD function or Distronic Plus* is activated.
X
Switch off HOLD (Y page 151) or Distronic Plus (Y page 146).
X Try to start the engine again. The engine will not
start. You can hear the
starter motor operat-
ing. R
There is a malfunction in the engine electronics.
R There is a malfunction in the fuel supply.
R The on-board voltage is too low because the starter battery is
too weak or discharged.
X Before the next start attempt, turn the key back to position 0
(Y page 75) in the ignition lock or press the Start/Stop but-
ton* until all the indicator lights in the instrument cluster have
gone out.
X Try to start the engine again (Y page 103). When doing so,
remember that excessively long and frequent attempts to start
the engine will drain the battery.
If the engine does not start after several attempts:
X Consult a qualified specialist workshop. The engine will not
start. You can hear the
starter motor operat-
ing. The reserve fuel
warning lamp is on and
the fuel gauge
shows
0. The fuel tank has been run dry.
X
Refuel the vehicle. The engine will not
start. You cannot hear
the starter motor. The on-board voltage is too low because the starter battery is too
weak or discharged.
X
Jump-start the vehicle (Y page 323).
If the engine does not start despite attempting to jump-start it:
X Consult a qualified specialist workshop. The starter motor was exposed to a thermal load that was too high.
X
Allow the starter motor to cool down for approximately two
minutes.
X Try to start the engine again.
If the engine still does not start:
X Consult a qualified specialist workshop. Troubleshooting
291Practical advice
* optional
212_AKB; 2; 4, en-GB
mkalafa,
Version: 2.11.8.1 2009-05-05T14:17:16+02:00 - Seite 291 Z
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:13; WK 

Problem
Possible causes/consequences and
X XSolutions Vehicles with a petrol
engine:
The engine is not run-
ning smoothly and is
misfiring. There is a malfunction in the engine electronics or a mechanical
component of the engine control unit.
X
Only depress the accelerator pedal slightly.
X Have the cause rectified immediately at a qualified specialist
workshop.
Otherwise, non-combusted fuel may get into the catalytic con-
verter and damage it. The coolant tempera-
ture gauge shows a
value above 120 †.
The coolant warning
lamp may also light up
and a warning tone may
sound (Y
page 117). 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 221). Observe the warning
notes as you do so and top up the coolant if necessary. If the coolant level is correct, the radiator fan may be faulty. The
coolant is too hot and the engine is no longer being cooled suffi-
ciently.
X
If the coolant temperature is less than 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 on
mountain roads and stop/start driving. 292
TroubleshootingPractical advice
212_AKB; 2; 4, en-GB
mkalafa,
Version: 2.11.8.1 2009-05-05T14:17:16+02:00 - Seite 292
Dateiname: 6515346702_buchblock.pdf; erzeugt am 07. May 2009 14:17:13; WK