check engine MERCEDES-BENZ GLS-Class SUV 2017 X166 Service Manual

Warning/
indicator
lampNSignal type
Possible causes/consequences and M
Solutions
F!NF (USA only), !(Canada only): the red indicator lamp for the electric
parking brake flashes or is lit and/or the yellow warning lamp for the electric
parking brake is lit.
XObserve the additional display messages in the multifunction display.
6N The red restraint system warning lamp is lit while the engine is running.
The restraint system is malfunctioning.
GWARNING
The air bags or Emergency Tensioning Devices may either be triggered uninten-
tionally or, in the event of an accident, may not be triggered.
There is an increased risk of injury.
XObserve the additional display messages in the multifunction display.
XDrive on carefully.
XContact a qualified specialist workshop and have the restraint system checked.
For further information about the restraint system, see (
Ypage 41).
282Warning and indicator lamps in the instrument cluster
On-board computer and displays

Engine
Warning/
indicator
lampNSignal type
Possible causes/consequences and M
Solutions
;NThe yellow Check Engine warning lamp lights up while the engine is running.
There may be a malfunction, for example:
Rin the engine management
Rin the fuel injection system
Rin the exhaust system
Rin the ignition system (for vehicles with gasoline engines)
Rin the fuel system
The emission limit values may be exceeded and the engine may be in emergency
mode.
XVisit a qualified specialist workshop immediately.
Vehicles with a diesel engine: the fuel tank has been run dry (
Ypage 156).
XStart 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.
In some states, you must immediately visit a qualified specialist workshop as soon
as the yellow Check Engine warning lamp lights up. This is due to the legal require-
ments in effect in these states. If in doubt, check whether such legal regulations
apply in the state in which you are currently driving.
8N The yellow reserve fuel warning lamp lights up while the engine is running.
The fuel level has dropped into the reserve range.
XRefuel at the nearest gas station.
8N The yellow reserve fuel warning lamp flashes while the vehicle is in motion.
In addition, the ;Check Engine warning lamp may light up.
The fuel filler cap is not closed correctly or the fuel system is leaking.
XCheck that the fuel filler cap is correctly closed.
XIf the fuel filler cap is not correctly closed: close the fuel filler cap.
XIf the fuel filler cap is closed:visit a qualified specialist workshop.
?NThe red coolant warning lamp lights up while the engine is running and the
coolant temperature gauge is at the start of the scale.
The temperature sensor for the coolant temperature gauge is malfunctioning.
The coolant temperature is no longer being monitored. There is a risk of engine
damage if the coolant temperature is too high.
XPull 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.
XSecure the vehicle against rolling away (Ypage 159).
XConsult a qualified specialist workshop.
Warning and indicator lamps in the instrument cluster283
On-board computer and displays
Z

Warning/
indicator
lampNSignal type
Possible causes/consequences and M
Solutions
?NThe red coolant warning lamp comes on while the engine is running.
The coolant level is too low.
If the coolant level is correct, the airflow to the engine radiator may be blocked or
the electric engine radiator fan may be defective.
The coolant is too hot and the engine is no longer being cooled sufficiently.
XObserve the additional display messages in the multifunction display.
XPull over and stop the vehicle safely and switch off the engine, paying attention
to road and traffic conditions.
XSecure the vehicle against rolling away (Ypage 159).
XLeave the vehicle and keep a safe distance from the vehicle until the engine has cooled down.
XCheck the coolant level and add coolant, observing the warning notes
(Ypage 322).
XIf you have to add coolant frequently, have the engine cooling system checked.
XMake sure that the air supply to the engine radiator is not blocked, e.g. by snow,
slush or ice.
XDo not start the engine again until the coolant temperature is below 248 ‡
(120 †). Otherwise, the engine could be damaged.
XDrive to the nearest qualified specialist workshop.
XAvoid heavy loads on the engine as you do so, e.g. driving in mountainous terrain
and stop-and-go traffic.
?N The red coolant warning lamp comes on while the engine is running.
The coolant temperature has exceeded 248 ‡ (120 †). The airflow to the engine
radiator may be blocked or the coolant level may be too low.
GWARNING
The engine is not being cooled sufficiently and may be damaged.
Do not drive when your engine is overheated. This can cause some fluids which
may have leaked into the engine compartment to catch fire.
Steam from the overheated engine can also cause serious burns which can occur
just by opening the hood.
There is a risk of injury.
XObserve the additional display messages in the multifunction display.
XPull over and stop the vehicle safely and switch off the engine, paying attention
to road and traffic conditions.
XSecure the vehicle against rolling away (Ypage 159).
XLeave the vehicle and keep a safe distance from the vehicle until the engine has
cooled down.
XCheck the coolant level and add coolant, observing the warning notes
(Ypage 322).
XIf you have to add coolant frequently, have the engine cooling system checked.
XMake sure that the air supply to the engine radiator is not blocked, e.g. by snow,
slush or ice.
284Warning and indicator lamps in the instrument cluster
On-board computer and displays

XMake sure that the windshield wipers are
turned off.
XPull release lever:on the hood.
The hood is released.
XReach into the gap, pull hood catch handle ;
up 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
XLower the hood and let it fall from a height of
approximately 8 in (20 cm).
XCheck 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
Important safety notes
GWARNING
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.
GWARNING
If engine oil comes into contact with hot com- ponents in the engine compartment, it may
ignite. There is a risk of fire and injury.
Make sure that engine oil is not spilled next to
the filler neck. Let the engine cool down and
thoroughly clean the engine oil off the com-
ponents before starting the engine.
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:
Rpark the vehicle on a level surface.
Rthe engine should be switched off for approx-
imately five minutes if the engine is at normal
operating temperature.
Rif the engine is not at normal operating tem-
perature, e.g. if the engine was only started
briefly, wait about 30 minutes before carrying
out the measurement.
320Engine compartment
Maintenance and care

Checking the oil level using the oil dip-
stick
Example:vehicle swit h a gasolin eengin e
Example :vehicle swit h a diesel engin e
XPull dipstick :out of the dipstick tube.
XWipe off oil dipstick :.
XSlowly slide oil dipstick :into the guide tube
to the stop, and take it out again.
If the level is between MIN mark =and MAX
mark ;, the oil level is correct.
XIf the oil level has dropped to MIN mark =or
below, add 1.1 US qt (1.0 liter) engine oil.
Adding engine oil
HEnvironmental note
When adding oil, take care not to spill any. If
oil enters the soil or waterways, it is harmful to
the environment.
!Use only engine oils and oil filters that are
approved for vehicles with a service system. A list of the engine oils and oil filters that have
been tested and approved in accordance with
Mercedes-Benz Specifications for Service
Products is available at any authorized
Mercedes-Benz Center. The following cause engine failure or damage
to the exhaust system:
RUse of engine oils and oil filters that have
not been expressly approved for the service
system
RReplacement of engine oil and oil filter after
the replacement interval specified by the
service system has expired
RUse of engine oil additives
!Do not add too much oil. adding too much
engine oil can result in damage to the engine
or to the catalytic converter. Have excess
engine oil siphoned off.
Example: engine oil cap
XTurn cap :counter-clockwise and remove it.
XAdd engine oil.
If the oil level is at or below the MIN mark on
the oil dipstick, add 1.1 US qt (1.0 liter) of
engine oil.
XReplace cap :on the filler neck and tighten
clockwise.
Ensure that the cap locks into place securely.
XCheck the oil level again with the oil dipstick
(Ypage 321).
Further information on engine oil (
Ypage 381).
Additional service products
Important safety notes
GWARNING
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.
Engine compartment321
Maintenance and care
Z

Where possible, let the engine cool down andtouch only the components described in the
following.
GWARNING
The cooling system is pressurized, particularly
when the motor is warm. If you open the cap,
you could be scalded if hot coolant sprays out.
There is a risk of injury.
Let the engine cool down before you open the
cap. Wear gloves and eye protection. Slowly
open the cap to relieve pressure.
GWARNING
Windshield washer concentrate could ignite if it comes into contact with hot engine compo-
nents or the exhaust system. There is a risk of
fire and injury.
Make sure that no windshield washer con-
centrate is spilled next to the filler neck.
Checking coolant level
XPark the vehicle on a level surface.
Only check the coolant level when the vehicle
is on a level surface and the engine has cooled
down.
XTurn the SmartKey to position 2in the ignition
lock (Ypage 138).
On vehicles with KEYLESS-GO, press the
Start/Stop button twice (
Ypage 140).
XCheck the coolant temperature gauge in the
multifunction display.
The coolant temperature must be below
158 ‡ (70 †).
XTurn the SmartKey to position 0in the ignition
lock (Ypage 138).
XOn vehicles with KEYLESS-GO, press the
Start/Stop button (Ypage 140).
XPress the Start/Stop button (Ypage 140).
XSlowly turn cap :half a turn counter-clock-
wise and allow excess pressure to escape.
XTurn cap :further counter-clockwise and
remove it.
If the coolant is at the level of marker bar =
in the filler neck when cold, there is enough
coolant in coolant expansion tank ;.
If the coolant level is approximately 0.6 in
(1.5 cm) above marker bar =in the filler neck
when warm, there is enough coolant in expan-
sion tank ;.
XIf necessary, add coolant that has been tested
and approved by Mercedes-Benz.
XReplace cap :and turn it clockwise as far as
it will go.
For further information on coolant, see
(
Ypage 382).
Adding washer fluid to the windshield
washer system
Example: washer fluid reservoir
XTo open: pull cap:upwards by the tab.
XAdd the premixed washer fluid.
XTo close: press cap :onto the filler neck
until it engages.
If the washer fluid level drops below the recom-
mended minimum of 1 liter, a message appears
in the multifunction display prompting you to
add washer fluid (
Ypage 273).
Further information on windshield washer fluid
(
Ypage 383).
322Engine compartment
Maintenance and care

XIf possible, bring the front wheels into the
straight-ahead position.
XVehicles with the AIRMATIC package:
make sure that the normal vehicle level is
selected (
Ypage 188).
XVehicles with the Off-Road Engineering
package:make sure that the normal level is
selected (
Ypage 182).
XSwitch off the engine.
XVehicles without KEYLESS-GO: remove the
SmartKey from the ignition lock.
XVehicles with KEYLESS-GO: open the driv-
er's door.
The on-board electronics now have status 0.
This is the same as the SmartKey having been
removed.
XVehicles with KEYLESS-GO: remove the
Start/Stop button from the ignition lock
(
Ypage 138).
XMake sure that the passengers are not endan-
gered as they do so. Make sure that no one is
near the danger area while a wheel is being
changed. Anyone who is not directly assisting in the wheel change should, for example,
stand behind the barrier.
XGet out of the vehicle. Pay attention to traffic
conditions when doing so.
XClose the driver's door.
XUnload heavy luggage.
iOnly operate the tire inflation compressor
using a 12 V socket, even if the ignition is
turned off (
Ypage 306).
An emergency cut-out ensures that the on-
board voltage does not drop too low. If the on-
board voltage is too low, the power to the
sockets is automatically cut. This ensures
that there is sufficient power to start the
engine.
MOExtended tires (tires with run-flat
properties)
General notes
With MOExtended tires (tires with run flat char-
acteristics), you can continue to drive your vehi-
cle even if there is a total loss of pressure in one
or more tires. The affected tire must not show
any clearly visible damage.
You can recognize MOExtended tires by the
MOExtended marking which appears on the sidewall of the tire. You will find this marking
next to the tire size designation, the load-bear-
ing capacity and the speed index (
Ypage 361).
MOExtended tires may only be used in conjunc-
tion with an active tire pressure loss warning
system or with an active tire pressure monitor.
If a pressure loss warning message appears
in the multifunction display:
Robserve the instructions in the display mes-
sages (Ypage 268).
Rcheck the tire for damage.
Rif driving on, observe the following notes.
The driving distance possible in run-flat mode is
approximately 50 miles (80 km) when the vehi-
cle is partially laden and approximately 18 miles
(30 km) when the vehicle is fully laden.
In addition to the vehicle load, the driving dis-
tance possible depends upon:
Rvehicle speed
Rroad condition
Routside temperature
The driving distance possible in run-flat mode
may be reduced by extreme driving conditions
or maneuvers, or it can be increased through a
moderate style of driving.
The driving distance possible in run-flat mode is
counted from the moment the tire pressure loss
warning appears in the multifunction display.
You must not exceed a maximum speed of
50 mph (80 km/h).
iWhen replacing one or all tires, please
observe the following specifications for your
vehicle's tires:
Rsize
Rtype and
Rthe "MOExtended" mark
If a tire has gone flat and cannot be replaced with a MOExtended tire, a standard tire may
be used as a temporary measure. Make sure
that you use the proper size and type (sum-
mer or winter tire).
iVehicles equipped with MOExtended tires
are not equipped with a TIREFIT kit at the fac-
tory. It is therefore recommended that you
additionally equip your vehicle with a TIR
EFIT
kit if you mount tires that do not feature run-
flat properties, e.g. winter tires. A TIREFIT kit
may be obtained from a qualified specialist
workshop.
332Flat tire
Breakdown assistance

The vehicle will then use very little energy, thus
conserving battery power.
If the power supply has been interrupted, e.g. ifyou reconnect the battery, you will have to:
Rset the clock; see the Digital Operator's Man-
ual
On vehicles with a multimedia system and
navigation system, the clock is set automati-
cally.
Rreset the function for folding the exterior mir-
rors in/out automatically, by folding the mir-
rors out once (
Ypage 108).
Charging the 12 V battery
GWARNING
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.
GWARNING
Battery acid is caustic. There is a risk of injury.
Avoid contact with skin, eyes or clothing. Do
not inhale any battery gases. Do not lean over
the battery. Keep children away from batter-
ies. Wash away battery acid immediately with
plenty of clean water and seek medical atten-
tion.
GWARNING
A discharged battery can freeze at tempera-
tures below freezing point. When jump-start-
ing 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 (
Ypage 338).
XOpen the hood.
XConnect 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 (
Ypage 338).
Keep away from fire and open flames. Do not
lean over a battery. Never charge the battery if it
is still installed in the vehicle, unless you use a
battery charger which has been tested and
approved by Mercedes-Benz. A battery charger
unit specially adapted for Mercedes-Benz vehi-
cles and tested and approved by Mercedes-
Benz is available as an accessory. 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.
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
For the jump-starting procedure, use only the jump-starting connection point in the engine com-
partment, consisting of a positive terminal and a ground point.
GWARNING
Battery acid is caustic. There is a risk of injury.
338Jump-starting
Breakdown assistance

Avoid contact with skin, eyes or clothing. Do not inhale any battery gases. Do not lean over the
battery. Keep children away from batteries. Wash away battery acid immediately with plenty of
clean water and seek medical attention.
GWARNING
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.
GWARNING
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.
RMake sure that the positive terminal of a connected battery does not come into contact with
vehicle parts.
RNever place metal objects or tools on a battery.
RIt is important that you observe the described order of the battery terminals when connecting
and disconnecting a battery.
RWhen jump-starting, make sure that the battery poles with identical polarity are connected.
RIt is particularly important to observe the described order when connecting and disconnecting
the jumper cables.
RNever connect or disconnect the battery terminals while the engine is running.
GWARNING
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. Otherwise, the
catalytic converter could be damaged by non-combusted fuel.
If the indicator/warning lamps do not light up at low temperatures, it is very 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 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:
RThe 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 de vice.
RVehicles with a gasoline engine:only jump-start the vehicle when the engine and exhaust
system are cold.
RDo not start the engine if the battery is frozen. Let the battery thaw first.
ROnly jump-start from batteries with a 12 V voltage rating.
ROnly use jumper cables which have a sufficient cross-section and insulated terminal clamps.
Jump-starting339
Breakdo wn assis tance
Z

RIf 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.
RMake sure that the two vehicles do not touch.
Make sure that:
RThe jumper cables are not damaged.
RBare parts of the terminal clamp do not come into contact with other metal parts while the jumper
cables are connected to the battery.
RThe 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.
XSecure the vehicle by applying the electric parking brake.
XShift the transmission to position P.
XMake sure that the ignition is switched off. All indicator lamps in the instrument cluster must be
off. When using the SmartKey, turn the SmartKey to position 0in the ignition lock and remove it
(
Ypage 138).
XSwitch off all electrical consumers, e.g. rear window defroster, lighting, etc.
XOpen the hood.
Position number Bidentifies the charged battery of the other vehicle or an equivalent jump-starting
device.
XSlide cover :of positive terminal ;in the direction of the arrow.
XConnect positive terminal ;on your vehicle to positive terminal =of donor battery Busing the
jumper cable, always begin with positive terminal ;on your own vehicle first.
XStart the engine of the donor vehicle and run it at idling speed.
XConnect negative terminal ?of donor battery Bto ground point Aof your vehicle using the
jumper cable, connecting the jumper cable to battery of other vehicle Bfirst.
XStart the engine.
XBefore disconnecting the jumper cables, let the engine run for several minutes.
XFirst, remove the jumper cables from ground point Aand negative terminal ?, then from pos-
itive clamp ;and positive terminal =. Begin each time at the contacts on your own vehicle first.
XClose cover:of positive terminal ;after removing the jumper cables.
XHave the battery checked at a qualified specialist workshop.
Jump-starting is not considered to be a normal operating condition.
340Jump-starting
Breakdown assistance