Engine MERCEDES-BENZ R-Class 2012 W251 Manual Online

Display messagesPossible causes/consequences and M Solutionsb
AUTO Light
InoperativeThe light sensor is defective.XVisit a qualified specialist workshop.
USA only:
XSwitch off the daytime running lamps in the on-board computer
( Y page 206).XSwitch the lights on and off using the light switch.b
Switch Off LightsThe lights are still switched on when you leave the vehicle. A
warning tone also sounds.XTurn the light switch to $ or à .
or
XIf the rear fog lamp is switched on: press the light switch in to
the stop.
Engine
Display messagesPossible causes/consequences and M Solutions+
Top Up Coolant See
Operator's ManualThe coolant level is too low.XAdd coolant, observing the warning notes when doing so
( Y page 285).XIf the coolant needs to be refilled more often than usual, have
the engine coolant system checked at a qualified specialist
workshop.GWARNING
Do not spill antifreeze on hot engine parts. Antifreeze contains ethylene glycol which may burn
if it comes into contact with hot engine parts. You could be seriously burned.
! The coolant level is too low. Avoid making long journeys with too little coolant in the cooling
system. The engine will otherwise be damaged.
The display messages and the corresponding symbol that indicate that the coolant level is
too low must not be ignored.
Display messages225On-board computer and displaysZ

Display messagesPossible causes/consequences and M Solutions?
Coolant Stop car,
switch engine offThe coolant is too hot.XPull over and stop the vehicle safely and switch off the engine,
paying attention to road and traffic conditions.XMake sure that the air supply to the engine radiator is not
blocked, e.g. by snow, slush or ice.XWait until the display message disappears before restarting the
engine. Otherwise, there is a risk of engine damage.XPay attention to the coolant temperature display.XIf the temperature increases again, visit a qualified specialist
workshop immediately.The poly-V-belt may have torn.XPull over and stop the vehicle safely and switch off the engine,
paying attention to road and traffic conditions.XOpen the hood.XCheck whether the poly-V-belt is torn.
If the poly-V-belt is torn:
! Do not continue driving. The engine could otherwise overheat.
XConsult a qualified specialist workshop.
If the poly-V-belt is OK:
XWait until the display message disappears before restarting the
engine. Otherwise, there is a risk of engine damage.XPay attention to the coolant temperature display.XVisit a qualified specialist workshop.GWARNING
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.
! If the coolant temperature exceeds 248 ‡(120 †) do not continue driving. The engine will
otherwise be damaged.
226Display messagesOn-board computer and displays

Display messagesPossible causes/consequences and M Solutions?The engine fan is defective.XAt coolant temperatures under 248 ‡ (120 †), drive to the next
qualified specialist workshop.XAvoid subjecting the engine to heavy loads, e.g. driving in
mountainous terrain, and stop-and-go traffic.#The battery is not being charged.
Possible causes are:
R a defective alternator
R a torn poly-V-belt
R a malfunction in the electronicsXPull over and stop the vehicle safely and switch off the engine,
paying attention to road and traffic conditions.XOpen the hood.XCheck whether the poly-V-belt is torn.
If the poly-V-belt is torn:
! Do not continue driving. The engine could otherwise overheat.
XConsult a qualified specialist workshop.
If the poly-V-belt is OK:
XVisit a qualified specialist workshop.#
Battery /
Alternator Stop
VehicleThe battery is defective.XPull over and stop the vehicle safely as soon as possible, paying
attention to road and traffic conditions. Do not continue driving
under any circumstances.XEngage the parking brake.XConsult a qualified specialist workshop.4
Check engine oil
level at next
refuelingThe oil level is too low.XCheck the oil level ( Y page 283).XIf necessary, add engine oil ( Y page 284).XHave the engine checked for leaks if the engine oil needs to be
refilled more often than usual.
Information on approved engine oils can be obtained from any qualified specialist workshop
or on the Internet at http://www.mbusa.com (USA only).
! The oil level is too low. Avoid long journeys with too little engine oil. There is a risk of
engine damage.
The display messages and the corresponding symbol that indicate that the oil level is too
low must not be ignored.
Display messages227On-board computer and displaysZ

Display messagesPossible causes/consequences and M Solutions8
Reserve FuelThe fuel level has dropped into the reserve range.XRefuel at the nearest gas station.CThere is only a very small amount of fuel in the fuel tank.XRefuel at the nearest gas station without fail.8
Gas Cap OpenThe fuel system pressure is too low. The fuel filler cap is not closed
correctly or the fuel system is leaking.XCheck that the fuel filler cap is correctly closed.
If the fuel filler cap is not correctly closed:
XClose the fuel filler cap.
If the fuel filler cap is correctly closed:
XVisit a qualified specialist workshop.8
Ultra Low-sulfur
Diesel Fuel OnlyVehicles with a diesel engine: the fuel level has fallen below the
reserve range.XRefuel at the nearest gas station.XOnly use commercially available vehicular ULTRA-LOW SULFUR
HIGHWAY DIESEL FUEL (ULSD, 15 ppm SULFUR MAXIMUM).¸
Replace air filterVehicles with a diesel engine: the engine air filter is dirty and must
be replaced.XVisit a qualified specialist workshop.·
Clean Fuel FilterVehicles with a diesel engine: there is water in the fuel filter. The
water must be drained off.XVisit a qualified specialist workshop.Ø
Check Additive See
Operator's ManualThe DEF tank is empty.XHave the DEF tank filled as soon as possible at a qualified
specialist workshop ( Y page 161).Ø
Remaining Starts:
16The DEF level has fallen to a minimum.XHave the DEF tank filled immediately at a qualified specialist
workshop. ( Y page 161)228Display messagesOn-board computer and displays

Display messagesPossible causes/consequences and M SolutionsBlind Spot Assist
Currently
Unavailable, See
Operator's ManualBlind Spot Assist is temporarily inoperative if:
R the sensors are dirty.
R its function is impaired due to heavy rain or snow.
R the radar sensor system is outside the operating temperature
range.
R the radar sensor system is temporarily inoperative, e.g. due to
electromagnetic radiation emitted by nearby TV or radio
stations or other sources of electromagnetic radiation.
The yellow 9 indicator lamps also light up in the exterior
mirrors.
Blind Spot Assist is operational again and the display message
disappears if:
R the dirt (e.g. slush) drops away while the vehicle is in motion.
R the system detects that the sensors are fully available again.
R the radar sensor system is back within the operating
temperature range.
If the display message continues to be displayed:XClean the sensors ( Y page 291).XRestart the engine.Blind Spot Assist
InoperativeBlind Spot Assist is defective.
The yellow 9 indicator lamps also light up in the exterior
mirrors.XVisit a qualified specialist workshop.Cruise Control
InoperativeCruise control is defective.XVisit a qualified specialist workshop.Cruise Control
--- MPH A condition for activating cruise control has not been fulfilled.
You attempted to save a speed of less than 20 mph (30 km/h).XIf the situation allows, drive faster than 20 mph ( 30 km/h) and
save the speed.XCheck the activation conditions for cruise control
( Y page 170).DISTRONIC
--- MPH An activation condition for DISTRONIC is not fulfilled.XCheck the activation conditions for DISTRONIC ( Y page 173).DISTRONIC
OverrideDISTRONIC is no longer controlling the speed of the vehicle.XTake your foot off the accelerator pedal.230Display messagesOn-board computer and displays

Display messagesPossible causes/consequences and M SolutionsDISTRONIC
InoperativeDISTRONIC is defective or the display has failed.XVisit a qualified specialist workshop.DISTRONIC
Currently
Unavailable See
Operator's ManualDISTRONIC is deactivated and is temporarily inoperative if:
R the DISTRONIC cover in the radiator grill is dirty.
R its function is impaired due to heavy rain, snow or fog.
R the radar sensor system is temporarily inoperative, e.g. due to
electromagnetic radiation emitted by nearby TV or radio
stations or other sources of electromagnetic radiation.
R the radar sensor system has not detected any vehicles or
stationary objects, e.g. traffic signs, for a long time.
R the system is outside the operating temperature range.
DISTRONIC becomes available again and the display message
disappears if:
R the dirt (e.g. slush) drops away while the vehicle is in motion.
R the system detects that the sensors are fully available again.
R the system is within the operating temperature range.
If the display message continues to be displayed:XClean the DISTRONIC cover in the radiator grill ( Y page 291).XRestart the engine.GWARNING
DISTRONIC cannot take weather conditions into account. Switch off DISTRONIC or do not turn
it on if the sensor is dirty or visibility is diminished as a result of snow, rain or fog. The distance
control may be impaired even before the system is able to detect a dirty sensor. The DISTRONIC
Currently Unavailable See Operator's Manual message will be displayed in the
multifunction display and DISTRONIC will be turned off.
Tires
GWARNING
Do not drive with a flat tire. A flat tire affects the ability to steer or brake the vehicle. You may
lose control of the vehicle. Continued driving with a flat tire will cause excessive heat build-up
and possibly a fire.
GWARNING
Follow recommended tire inflation pressures.
Do not underinflate tires. Underinflated tires wear excessively and/or unevenly, adversely affect
handling and fuel economy, and are more likely to fail from being overheated.
Display messages231On-board computer and displaysZ

Display messagesPossible causes/consequences and M Solutionsh
Tire Pressure
Check TiresGRisk of accident
The tire pressure in one or more tires has dropped significantly.
XStop the vehicle without making any sudden steering or braking
maneuvers. Pay attention to the traffic conditions as you do so.XIf necessary, change a wheel ( Y page 346).XCheck the tire pressure. If necessary, correct the tire pressure
( Y page 331).h
Please correct the
tire pressuresThe tire pressure is too low in at least one of the tires or the tire
pressure difference between the wheels is too great.XCheck the tire pressures at the next opportunity. If necessary,
correct the tire pressure ( Y page 331).
Vehicle
Display messagesPossible causes/consequences and M SolutionsShift to P or N
to start engine.You have attempted to start the engine with the transmission in
position R or D.XShift the transmission to position P or N.Auxiliary Battery
MalfunctionThe auxiliary battery for the automatic transmission is no longer
being charged.XVisit a qualified specialist workshop at the next opportunity.XUntil then, set the automatic transmission to position P before
you switch off the engine.XBefore leaving the vehicle, apply the parking brake.Depress brake to
shift out of P.You have attempted to move the transmission selector lever to
position D, R or N without depressing the brake pedal.XDepress the brake pedal.Door Open
Vehicle Not In ParkThe driver's door is open and the transmission is in position R, N
or D.XShift the transmission to position P.XEngage the parking brake.234Display messagesOn-board computer and displays

Display messagesPossible causes/consequences and M Solutions~
Bluetooth readyThe Bluetooth ®
connection between your mobile phone and
COMAND is not activated.XIf desired, activate the Bluetooth ®
connection between your
mobile phone and COMAND (see the separate Operator's
Manual).¥
Top Up Washer FluidThe washer fluid level has dropped to approximately ⅓ of the total
reservoir capacity.XAdd washer fluid ( Y page 285).
SmartKey
Display messagesPossible causes/consequences and M Solutions+
Key Does Not
Belong to VehicleYou have put the wrong SmartKey in the ignition lock.XUse the correct SmartKey.+
Remove KeyThe SmartKey is in the ignition lock.XRemove the SmartKey.+
You need a new key.The SmartKey needs to be replaced.XVisit a qualified specialist workshop.+
Change Key
BatteriesThe batteries of the KEYLESS-GO key are discharged.XChange the batteries ( Y page 76).+
Don't Forget Your
KeyThe display message is shown for a maximum of 60 seconds and
is only a reminder.
You have opened the driver's door with the engine switched off.
The KEYLESS-GO key is not in the ignition lock.XRemember to take the KEYLESS-GO key with you when you
leave the vehicle.236Display messagesOn-board computer and displays

Display messagesPossible causes/consequences and M Solutions+
Key Not Detected
(Red display message)The KEYLESS-GO key is not in the vehicle.
If the engine is switched off, you can no longer lock the vehicle
centrally or start the engine.XPull over and stop the vehicle safely as soon as possible, paying
attention to road and traffic conditions.XEngage the parking brake.XLocate the KEYLESS-GO key.The KEYLESS-GO key is not detected while the engine is running
because there is interference from a strong source of radio waves.XPull over and stop the vehicle safely as soon as possible, paying
attention to road and traffic conditions.XEngage the parking brake.XOperate the vehicle with the SmartKey in the ignition lock.+
Key Not Detected
(White display
message)The KEYLESS-GO key cannot be detected at present.XChange the location of the key with the KEYLESS-GO functions
in the vehicle.
If the KEYLESS-GO key is still not detected:
XChange the location of the key with the KEYLESS-GO functions
in the vehicle.XOperate the vehicle with the SmartKey in the ignition lock.+
Key Detected in
VehicleThe KEYLESS-GO key has been detected inside the vehicle during
locking.XRemove the KEYLESS-GO key from the vehicle.+
Pull starting
button out then
insert key.The KEYLESS-GO key can continuously not be detected.XInsert the SmartKey into the ignition lock and turn it to the
desired position.XVisit a qualified specialist workshop.Display messages237On-board computer and displaysZ

Warning and indicator lamps in the instrument cluster
Seat belts
ProblemPossible causes/consequences and M Solutions7
After starting the
engine, the red seat
belt warning lamp lights
up for six seconds.The seat belt warning lamp reminds the driver and front passenger
to fasten their seat belts.XFasten your seat belt ( Y page 51).7
After starting the
engine, the red seat
belt warning lamp lights
up. In addition, a
warning tone sounds
for up to six seconds.GRisk of injury
The driver's seat belt is not fastened.
XFasten your seat belt ( Y page 51).
The warning tone ceases.7
The red seat belt
warning lamp lights up
after the engine starts,
as soon as the driver's
or the front-passenger
door is closed.GRisk of injury
The driver or front passenger has not fastened their seat belt.
XFasten your seat belt ( Y page 51).
The warning lamp goes out.GRisk of injury
There are objects on the front-passenger seat.
XRemove the objects from the front-passenger seat and stow
them in a secure place.
The warning lamp goes out.238Warning and indicator lamps in the instrument clusterOn-board computer and displays