check engine light MERCEDES-BENZ M-Class 2015 W166 Owner's Guide

of the towing vehicle, as the latter is equip-
ped with an anti-lock brake system. Doing
so will result in a loss of function of the
brake systems of both the vehicle and the
trailer.
X Make sure that the automatic transmission
is set to position P.
X Apply the vehicle's electric parking brake.
X Start the engine.
X Vehicles with the AIRMATIC package:
select highway level.
X Vehicles with ADS: set ADS toAUTOor
COMF.
X Switch off the engine.
X Close all doors and the tailgate.
X Couple up the trailer.
X Establish all electrical connections.
X Check that the trailer lighting system is
working.
i Vehicles with the AIRMATIC package:
with a trailer attached, the vehicle will
always remain at highway level. When cou-
pling up a trailer, please observe the fol-
lowing:
R Unless highway level has been set man-
ually, the vehicle is automatically low-
ered to highway level. This is the case if a
speed of 5 mph (8 km/h) is reached.
R High-speed level is not available.
These restrictions apply to all accessories
powered through a connection to the trailer power socket of your vehicle, e.g. a bicycle
carrier.
Observe the maximum permissible trailer
dimensions (width and length).
Most U.S. states and all Canadian provinces
require by law:
R Safety chains between the towing vehicle
and the trailer. The chains should be cross-
wound under the trailer drawbar. They must be fastened to the vehicle's trailer cou-
pling, not to the bumper or the axle. Leave enough play in the chains to make
tight cornering possible.
R A separate brake system for certain types
of trailer.
R A safety switch for braked trailers. Check
the specific legal requirements applicable
to your state.
If the trailer detaches from the towing vehi- cle, the safety switch applies the trailer's
brakes. Towing a trailer
There are numerous legal requirements con-
cerning the towing of a trailer, e.g. speed
restrictions. Make sure that your car/trailer
combination complies with the local regula-
tions: R in your place of residence
R in the location to which you are driving
The police and local authorities can provide
reliable information.
Observe the following when towing a trailer:
R To gain driving experience and to become
accustomed to the new handling charac-
teristics, you should practice the following
in a traffic-free location:
- cornering
- stopping
- backing up
R Before driving, check:
- trailer tow hitch
- safety switch for braked trailers
- safety chains
- electrical connections
- lights
- wheels
R Adjust the exterior mirrors to provide an
unobstructed view of the rear section of the trailer.
R If the trailer has electronically controlled
brakes, pull away carefully. Brake manually 260
Towing a trailerDriving and parking

using the brake controller and check
whether the brakes function correctly.
R Secure any objects on the trailer to prevent
the cargo from slipping when the vehicle is
in motion.
R When you couple up a trailer, check at reg-
ular intervals that the load is firmly secured.If the trailer is equipped with trailer lights
and brakes, check the trailer to ensure that
these are working.
R Bear in mind that the handling will be less
stable when towing a trailer than when driv- ing without one. Avoid sudden steering
movements.
R The vehicle/trailer combination is heavier,
accelerates more slowly, has a decreased
gradient climbing capability and a longer
braking distance.
It is more susceptible to side winds and
requires more careful steering.
R If possible, do not brake suddenly, but
instead depress the brake pedal moder-
ately at first so that the trailer can activate its brakes. Then increase the pressure on
the brake pedal.
R If the automatic transmission repeatedly
shifts between gears on uphill or downhill
gradients, shift to a lower gear using the
left-hand steering wheel paddle shifter.
A lower gear and lower speed reduce the
risk of engine failure.
R When driving downhill, shift to a lower gear
to utilize the engine's braking effect.
Avoid continuous brake application as this
may overheat the vehicle brakes and, if
installed, the trailer brakes.
R If the coolant temperature increases dra-
matically while the air-conditioning system
is switched on, switch off the air-condition-
ing system.
Coolant heat can also be dissipated by
opening the windows and switching the ventilation blower and the interior temper-
ature to the highest level.
R When overtaking, pay particular attention
to the extended length of your vehicle/
trailer combination.
Due to the length of the vehicle/trailer
combination, you require additional road
space in relation to the vehicle you are
overtaking before you can change back to
the original lane. Decoupling a trailer
G
WARNING
If you uncouple a trailer with the overrun
brake engaged, you could trap your hand
between the vehicle and the trailer drawbar.
There is a risk of injury.
Do not uncouple a trailer if the overrun brake is engaged. G
WARNING
Vehicles with level control:
The vehicle is lowered as soon as you discon-
nect the trailer cable. This could result in your limbs or those of other people that are
between the vehicle body and tires or under-
neath the vehicle being trapped. There is a
risk of injury.
Make sure that nobody is in the immediate
vicinity of the wheel housings or under the
vehicle when you disconnect the trailer cable.
! Do not disconnect a trailer with an
engaged overrun brake. Otherwise, your
vehicle could be damaged by the rebound- ing of the overrun brake.
X Make sure that the automatic transmission
is set to position P.
X Apply the vehicle's electric parking brake.
X Start the engine.
X Close all doors and the tailgate.
X Apply the trailer's parking brake. Towing a trailer
261Driving and parking Z

Useful information
i This Operator's Manual describes all
models and all standard and optional equip- ment 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 special-
ist workshops (Y page 29). Important safety notes
G
WARNING
If you operate information systems and com-
munication equipment integrated in the vehi- cle 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 equip-
ment when the vehicle is stationary. G
WARNING
If the instrument cluster has failed or mal-
functioned, 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 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 35). 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 located on the bottom left of the instrument cluster
(Y page 35).
X Turn the brightness control knob clockwise
or counter-clockwise.
If the light switch is set to 0058,0060or
0058, 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
Opening the hood when the engine is over-
heated or when there is a fire in the engine
compartment could expose you to hot gases
or other service products. There is a risk of
injury.
Let an overheated engine cool down before
opening the hood. If there is a fire in the
engine compartment, keep the hood closed
and contact the fire department.
! A display message is shown if the coolant
temperature is too high.
If the coolant temperature is over 248 ‡
(120 †), do not continue driving. The
engine will otherwise be damaged. 266
Displays and operationOn-board computer and displays

Display messages
Possible causes/consequences and
0050
0050Solutions 0049
Auto Auto
Lamp
LampFunction
Function
Inoperative
Inoperative The light sensor is defective.
X Visit a qualified specialist workshop. 0049
Switch Off Lights 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 0058.Adaptive Highbeam Adaptive Highbeam
Assist Inoperative Assist Inoperative Adaptive Highbeam Assist is faulty.
X
Visit a qualified specialist workshop. Adaptive Highbeam Adaptive Highbeam
Assist Currently Assist Currently
Unavailable See Unavailable See
Operator's Manual Operator's Manual Adaptive Highbeam Assist is deactivated and temporarily inoper-
ative. 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
Adaptive Highbeam Assist Now Available message is dis-
played.
Adaptive Highbeam Assist is operational again. Engine
Display messages
Possible causes/consequences and
0050 0050Solutions 00BD
Check Coolant Check Coolant
Level See Opera‐ Level See Opera‐
tor's Manual tor'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 369).
X If coolant needs to be added more often than usual, have the
engine coolant system checked at a qualified specialist work-
shop. 00AC 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 moun-
tainous terrain, and stop-and-go traffic. 300
Display
messagesOn-board computer and displays

Problem
Possible causes/consequences and
0050
0050Solutions 0049
(USA only)
0024 (Canada only)
The red electric parking brake indicator lamp
flashes or lights up
and/or
0024
warning lamp for the
electric parking brake
lights up. X
Observe the additional display messages in the multifunction
display. 0075
The red restraint sys-
tem warning lamp is lit
while the engine is run-
ning.
The restraint system is faulty.
G WARNING
The air bags or Emergency Tensioning Devices may either be trig- gered unintentionally or, in the event of an accident, may not be
triggered.
There is an increased risk of injury.
X Observe the additional display messages in the multifunction
display.
X Drive on carefully.
X Have the restraint system checked at a qualified specialist
workshop immediately.
For further information about the restraint system, see
(Y page 44). 326
Warning and indicator lamps in the instrument clusterOn-board computer and displays

Engine
Problem
Possible causes/consequences and
0050
0050Solutions 00B9
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 (for vehicles with gasoline engines)
R in the fuel system
The emission limit values may be exceeded and the engine may be
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 special-
ist workshop as soon as the yellow Check Engine warning lamp
lights up. This is due to the legal requirements in effect in these
states. If in doubt, check whether such legal regulations apply in the state in which you are currently driving. Vehicles with a diesel engine: the fuel tank has been run dry
(Y
page 180).
X Start the engine three to four times after refueling.
If the yellow Check Engine warning lamp goes out, emergency
running mode is canceled. The vehicle need not be checked. 00B6
The yellow reserve fuel
warning lamp lights up
while the engine is run-
ning.
The fuel level has dropped into the reserve range.
X Refuel at the nearest gas station. 00B6
The yellow reserve fuel
warning lamp flashes
while the vehicle is in
motion.
In addition, the
00B9
Check Engine warning
lamp may light up. 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 work-
shop. Warning and indicator lamps in the instrument cluster
327On-board computer and displays Z

!
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
turned off.
X Pull release lever 0043on the hood.
The hood is released. X
Reach into the gap, pull hood catch han-
dle 0044up and lift the hood.
If you lift the hood by approximately 15 in
(40 cm), the hood is opened and held open automatically by the gas-filled strut.
Closing the hood 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. Open it again and close
it with a little more force. Radiator
Vehicles with a diesel engine: do not cover
the radiator, for example with a winter front or bug cover. The readings of the on-board-diag-
nostic system may otherwise be inaccurate.
Some of these readings are required by law
and must be accurate at all times. Engine oil
General notes Depending on your driving style, the vehicle
consumes up to 0.9 US qt (0.8 liters) of oil per
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.
Checking the oil level using the oil dip-
stick G
WARNING
Certain components in the engine compart-
ment, such as the engine, radiator and parts
of the exhaust system, can become very hot.
Working in the engine compartment poses a
risk of injury.
Where possible, let the engine cool down and touch only the components described in the
following. Engine compartment
367Maintenance and care Z

!
Only use battery chargers with a maxi-
mum charging voltage of 14.8 V.
! Only charge the battery using the jump-
starting connection point.
If, at low temperatures, the indicator lamps/
warning lamps in the instrument cluster do
not light up, it is highly likely that the dis-
charged 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 charac-
teristics can be impaired, particularly at low
temperatures. Have the thawed-out battery
checked at a qualified specialist workshop.
Never charge a battery still installed in the
vehicle unless a battery charger unit
approved by Mercedes-Benz is being used. An
accessory battery charge unit specially adap- ted 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 informa-
tion and availability. Charge the battery in
accordance with the separate instructions for the battery charger.
The jump-starting connection point is in the
engine compartment (Y page 391).
Read the battery charger's operating instruc- tions before charging the battery.
X Open the hood.
X Connect the battery charger to the positive
terminal and ground point in the same
order as when connecting the donor bat-
tery in the jump-starting procedure
(Y page 391). 390
Battery (vehicle)Breakdown assistance

Jump-starting
For the jump-starting procedure, use only the jump-starting connection point, consisting of a positive terminal and a ground point, in the engine compartment. 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
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 ven-
tilation while charging and jump-starting. Do not lean over a battery. G
WARNING
During the charging process, a battery produces hydrogen gas. If a short circuit occurs or sparks
are created, the hydrogen gas can ignite. There is a risk of an explosion.
R Make sure that the positive terminal of a connected battery does not come into contact with
vehicle parts.
R Never place metal objects or tools on a battery.
R It is important that you observe the described order of the battery terminals when connecting
and disconnecting a battery.
R When jump-starting, make sure that the battery poles with identical polarity are connected.
R It is particularly important to observe the described order when connecting and disconnecting
the jumper cables.
R Never connect or disconnect the battery terminals while the engine is running. 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.
! Vehicles with a gasoline engine:
avoid repeated and lengthy starting attempts. Other-
wise, the catalytic converter could be damaged by non-combusted fuel.
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. Jump-starting
391Breakdown assistance Z