MERCEDES-BENZ M-Class 2015 W166 Workshop Manual

The shoulder section of the seat belt must
always be routed across the center of the
shoulder. Adjust the belt sash guide if neces-
sary.
X To raise: slide the belt guide upwards.
The belt guide will engage in various posi-
tions.
X To lower: hold belt guide release 0043and
slide the belt guide downwards.
X Let go of belt guide release 0043in the
desired position and make sure that the
belt guide engages.
All seat belts except the driver's seat belt are equipped with a special seat belt retractor to
securely fasten child restraint systems in the
vehicle. Further information can be found
under "Special seat belt retractor"
(Y page 61).
Releasing seat belts !
Make sure that the seat belt is fully rolled
up. Otherwise, the seat belt or belt tongue
will be trapped in the door or in the seat
mechanism. This could damage the door,
the door trim panel and the seat belt. Dam-
aged seat belts can no longer fulfill their
protective function and must be replaced.
Visit a qualified specialist workshop. X
Press release button 0043, hold belt
tongue 0044and guide it back towards belt
outlet 0087.
Seat belt adjustment The seat-belt adjustment is an integral part of
the PRE-SAFE ®
convenience function. This
function adjusts the driver's and front-
passenger seat belt to the upper body of the
occupants.
The belt strap is tightened slightly when:
R the belt tongue is engaged in the buckle
and
R the ignition is switched on
The seat-belt adjustment will apply a certain
tightening force if any slack is detected
between the vehicle occupant and the seat
belt. Do not hold on to the seat belt tightly
while it is adjusting.
You can switch the seat-belt adjustment on
and off in the on-board computer
(Y page 280).
Belt warning for the driver and front
passenger The
0076 seat belt warning lamp in the instru-
ment cluster is a reminder that all occupants
must fasten their seat belts. It may light up
continuously or flash. In addition, there may
be a warning tone.
Regardless of whether the driver's and front- passenger seat belts have already been fas-
tened, the 0076seat belt warning lamp lights
up for six seconds each time the engine is
started. If, after six seconds, the driver or
front-passenger seat belt has not been fas-
tened and the doors are closed, the 0076seat
belt warning lamp lights up. As soon as the
driver's and front-passenger seat belts are
fastened or a front door is opened again, the
0076 seat belt warning lamp goes out.
If the driver's seat belt is not fastened after
the engine is started, an additional warning
tone will sound. This warning tone stops after Occupant safety
49Safety Z

six seconds or when the driver's seat belt is
fastened.
If the vehicle's speed exceeds 15 mph
(25 km/h) once and the driver's and front-
passenger seat belts are not fastened, a
warning tone sounds. A warning tone also
sounds with increasing intensity for
60 seconds or until the driver or front
passenger have fastened their seat belts.
If the driver or front passenger unfasten their seat belts during the journey, the seat belt
warning is activated again.
i For more information on the
0076seat
belt warning lamp, see "Warning and indi-
cator lamps in the instrument cluster, seat
belts" (Y page 318). Air bags
Introduction The installation point of an air bag can be rec-
ognized by the AIR BAG symbol.
An air bag complements the correctly fas-
tened seat belt. It is no substitute for the seat
belt. The air bag provides additional protec-
tion in applicable accident situations.
Not all air bags are deployed in an accident.
The different air bag systems function inde-
pendently from one another (Y page 58).
However, no system available today can com- pletely eliminate injuries and fatalities.
It is also not possible to rule out a risk of injury
caused by an air bag due to the high speed at which the air bag must be deployed.
Important safety notes G
WARNING
If you do not sit in the correct seat position,
the air bag cannot protect as intended and
could even cause additional injury when
deployed. This poses an increased risk of
injury or even fatal injury. To avoid hazardous situations, always make
sure that all of the vehicle's occupants:
R have fastened their seat belts correctly,
including pregnant women
R are sitting correctly and maintain the great-
est possible distance to the air bags
R follow the following instructions
Always make sure that there are no objects
between the air bag and the vehicle's occu-
pants.
R Adjust the seats properly before beginning
your journey. Always make sure that the
seat is in an almost upright position. The
center of the head restraint must support
the head at about eye level.
R Move the driver's and front-passenger
seats as far back as possible. The driver's
seat position must allow the vehicle to be
driven safely.
R Only hold the steering wheel on the out-
side. This allows the air bag to be fully
deployed.
R Always lean against the backrest while driv-
ing. Do not lean forwards or lean against
the door or side window. You may other-
wise be in the deployment area of the air
bags.
R Always keep your feet in the footwell in
front of the seat. Do not put your feet on the
dashboard, for example. Your feet may oth- erwise be in the deployment area of the air
bag.
R For this reason, always secure persons less
than 5 ft (1.50 m) tall in suitable restraint
systems. Up to this height, the seat belt
cannot be worn correctly.
If a child is traveling in your vehicle, also
observe the following notes:
R Always secure children under 12 years of
age and less than 5 ft (1.50 m)in height in
suitable child restraint systems.
R Child restraint systems should be installed
on the rear seats. 50
Occupant safetySafety

R
Only secure a child in a rearward-facing
child restraint system to the front-
passenger seat when the front-passenger
front air bag is disabled. If the PASSENGER
AIR BAG OFF indicator lamp is permanently
lit, the front-passenger front air bag is dis-
abled (Y page 45).
R Always observe the instructions and safety
notes on the "Occupant Classification Sys-
tem (OCS)" (Y page 53) and on "Children
in the vehicle" (Y page 61) in addition to
the child restraint system manufacturer's
installation instructions.
Objects in the vehicle interior may pre-
vent the air bag from functioning cor-
rectly. Before starting your journey and to
avoid risks resulting from the speed of the air bag as it deploys, make sure that:
R there are no people, animals or objects
between the vehicle occupants and an air
bag.
R there are no objects between the seat, door
and B-pillar.
R no hard objects, e.g. coat hangers, hang on
the grab handles or coat hooks.
R no accessories, such as cup holders, are
attached to the vehicle within the deploy-
ment area of an air bag, e.g. to doors, side windows, rear side trim or side walls.
R no heavy, sharp-edged or fragile objects
are in the pockets of your clothing. Store
such objects in a suitable place. G
WARNING
If you modify the air bag cover or affix objects
such as stickers to it, the air bag can no longer function correctly. There is an increased risk
of injury.
Never modify an air bag cover or affix objectsto it. G
WARNING
Sensors to control the air bags are located in the doors. Modifications or work not per-
formed correctly to the doors or door panel-
ing, as well as damaged doors, can lead to the function of the sensors being impaired. The air
bags might therefore not function properly
any more. Consequently, the air bags cannot
protect vehicle occupants as they are
designed to do. There is an increased risk of
injury.
Never modify the doors or parts of the doors.
Always have work on the doors or door pan-
eling carried out at a qualified specialist work- shop.
Front air bags Driver's air bag
0043inflates in front of the
steering wheel; front-passenger air bag 0044
inflates in front of and above the glove box.
When deployed, the front air bags offer addi-
tional head and thorax protection on the front
seats.
The PASSENGER AIR BAG OFF indicator lamp shows you the status of the front-passenger
front air bag (Y page 45).
Front-passenger air bag 0044is only deployed
if:
R the Occupant Classification System (OCS)
recognizes that the front-passenger seat is
occupied (Y page 53)
R the PASSENGER AIR BAG OFF indicator
lamp is not lit (Y page 53)
R the restraint system control unit predicts a
high accident severity Occupant safety
51Safety Z

Driver's knee bag
Driver's knee bag
0043deploys under the steer-
ing column. The driver's knee bag is triggered
together with the front air bag.
The driver's knee bag offers additional thigh,
knee and lower leg protection for the occu-
pant in the driver's seat.
Side impact air bags G
WARNING
Unsuitable seat covers could restrict or even
prevent the deployment of the air bags inte-
grated into the seats. Consequently, the air
bags cannot protect vehicle occupants as
they are designed to do. In addition, the func- tion of the Occupant Classification System
(OCS) could be restricted. This poses an
increased risk of injury or even fatal injury.
You should only use seat covers that have
been approved for the respective seat by
Mercedes-Benz. Front side impact air bags
0043and rear side
impact air bags 0044inflate next to the outer
cushions of the seat backrest.
When deployed, the side impact air bag offers additional protection for the thorax. Further-
more, on the front seats additional protection
is offered for the pelvis. However, it does not protect your:
R head
R neck
R arms
In the event of a side impact, the side impact
air bag is deployed on the side on which an
impact occurs.
The side impact air bag on the front-
passenger side (front) deploys in the follow-
ing situations:
R the OCS system detects that the front-
passenger seat is occupied, or
R the belt tongue is engaged in the buckle on
the front-passenger seat
If the belt tongue is engaged in the buckle on the front-passenger seat, the side impact air
bag on the front-passenger side deploys at
the onset of the applicable accident situation. In this case, it will deploy regardless of
whether the front-passenger seat is occupied
or not.
Window curtain air bags Window curtain air bags
0043are integrated
into the side of the roof frame and deploy in
the area from the A-pillar to the C-pillar. 52
Occupant safetySafety

When deployed, the window curtain air bag
offers additional protection for the head.
However, it does not protect your chest or
arms.
In the event of a side impact, the window cur-
tain air bag is deployed on the side on which
the impact occurs.
If the system determines that window curtain air bag deployment can offer additional pro-
tection to that provided by the seat belt, a
window curtain air bag may deploy in other
accident situations (Y page 58).Occupant Classification System
(OCS)
Introduction The Occupant Classification System (OCS)
categorizes the person in the front-passenger
seat. Depending on that result, the front-
passenger front air bag is either enabled or
deactivated.
The system does not deactivate:
R the side impact air bag
R the window curtain air bag
R the Emergency Tensioning Devices
In the following situation, the side impact air
bag and Emergency Tensioning Device are
disabled: the OCS system detects that the
front-passenger seat is occupied, but the seat belt tongue is not inserted in the belt buckle
of the front-passenger seat.
Prerequisites To be classified correctly, the front passenger
must sit:
R with the seat belt fastened correctly
R in an almost upright position with their
back against the seat backrest
R with their feet resting on the floor, if possi-
ble If the front passenger does not observe these
conditions, OCS may produce a false classi-
fication, e.g. because the front passenger:
R transfers their weight by supporting them-
selves on a vehicle armrest
R sits in such a way that their weight is raised
from the seat cushion
If it is absolutely necessary to install a child
restraint system on the front-passenger seat,
be sure to observe the correct positioning of
the child restraint system. Never place
objects under or behind the child restraint
system, e.g. cushions. The entire base of the
child restraint system must always rest on the
seat cushion of the front-passenger seat. The
backrest of the forwards-facing child restraint system must, as far as possible, be resting on
the backrest of the front-passenger seat.
The child restraint system must not touch the roof or be put under strain by the head
restraint. Adjust the angle of the seat back-
rest and the head restraint position accord-
ingly.
Only then can OCS be guaranteed to function correctly. Always observe the child restraint
system manufacturer's installation instruc-
tions.
Occupant Classification System opera-
tion (OCS) PASSENGER AIR BAG OFF indicator lamp
0043
informs you whether the front-passenger
front air bag is deactivated.
X Turn the SmartKey to position 1or 2in the
ignition lock, or press the Start/Stop but- Occupant safety
53Safety Z

ton once or twice on vehicles with KEY-
LESS-GO.
The system carries out a self-diagnosis.
The PASSENGER AIR BAG OFF indicator lamp
must light up for approximately six second s.
The PA SSENGER AIR BAG OFF indicator lamp
then displays the status of the front-
passenger front air bag. If the status of the
front-passenger front air bag changes while
the vehicle is in motion, an air bag display
message may appear in the instrument clus-
ter (Y page 295). When the front-passenger
seat is occupied, always pay attention to the
PASSENGER AIR BAG OFF indicator lamp. Be aware of the status of the front-passenger
front air bag both before and during the jour-ney.
If the PASSENGER AIR BAG OFF indicator
lamp:
R is lit, the front-passenger front air bag is
deactivated. They will then not be deployed in the event of an accident.
R does not light up: the front-passenger
front air bag is enabled. If, in the event of an
accident, all deployment criteria are met,
the front-passenger front air bag is
deployed. G
WARNING
If the PASSENGER AIR BAG OFF indicator
lamp is lit, the front-passenger front air bag is disabled. It will not be deployed in the event of
an accident and cannot perform its intended
protective function. A person in the front-
passenger seat could then, for example, come
into contact with the vehicle's interior, espe-
cially if the person is sitting too close to the
dashboard. This poses an increased risk of
injury or even fatal injury.
When the front-passenger seat is occupied,
always ensure that:
R the classification of the person in the front-
passenger seat is correct and the front-
passenger front air bag is enabled or disa- bled in accordance with the person in the
front-passenger seat
R the front-passenger seat has been moved
back as far back as possible.
R the person is seated correctly.
Make sure, both before and during the jour-
ney, that the status of the front-passenger
front air bag is correct. G
WARNING
If you secure a child in a child restraint system on the front-passenger seat and the
PASSENGER AIR BAG OFF indicator lamp is
off, the front-passenger front air bag can
deploy in the event of an accident. The child
could be struck by the air bag. This poses an
increased risk of injury or even fatal injury.
Make sure that the front-passenger front air
bag has been disabled. The PASSENGER AIR
BAG OFF indicator lamp must be lit. G
WARNING
If you secure a child in a forward-facing child
restraint system on the front-passenger seat
and you position the front-passenger seat too close to the dashboard, the child could, in the
event of an accident:
R come into contact with the vehicle's inte-
rior if the PASSENGER AIR BAG OFF indi-
cator lamp is lit, for example
R be struck by the air bag if the PASSENGER
AIR BAG OFF indicator lamp is off
This poses an increased risk of injury or even
fatal injury.
Move the front-passenger seat as far back as possible. Always make sure that the shoulder
belt strap is correctly routed from the vehicle
belt sash guide to the shoulder belt guide on
the child restraint system. The shoulder belt
strap must be routed forwards and down-
wards from the vehicle belt sash guide. If nec- essary, adjust the vehicle belt sash guide and
the front-passenger seat accordingly. Always
observe the child restraint system manufac-
turer's installation instructions. 54
Occupant safetySafety

If OCS determines that:
R the front-passenger seat is unoccupied, the
PASSENGER AIR BAG OFF indicator lamp
lights up after the system self-test and
remains lit. This indicates that the front-
passenger front air bag is deactivated.
R the front-passenger seat is occupied by a
child of up to 12 months old, in a standard
child restraint system, the PASSENGER AIR BAG OFF indicator lamp lights up after the
system self-test and remains lit. This indi-
cates that the front-passenger front air bag
is deactivated.
But in the case of a 12-month-old child, in a standard child restraint system, the
PASSENGER AIR BAG OFF indicator lamp
can go out after the system self-test. This
indicates that the front-passenger front air
bag is activated. The result of the classifi-
cation is dependent on, among other fac-
tors, the child restraint system and the
child's stature. It is recommended that you
install the restraint system on a suitable
rear seat.
R the front-passenger seat is occupied by a
person of smaller stature (e.g. a teenager
or small adult), the PASSENGER AIR BAG
OFF indicator lamp lights up and remains lit after the system self-test depending on the result of the classification or, alternatively,
goes out.
- if the PASSENGER AIR BAG OFF indicator
lamp is off, move the front-passenger
seat as far back as possible. Alterna-
tively, a person of small stature can sit on
a rear seat.
- if the PASSENGER AIR BAG OFF indicator
lamp is lit, a person of smaller stature
should not use the front-passenger seat.
R the front-passenger seat is occupied by an
adult or a person of a stature correspond-
ing to that of an adult, the PASSENGER AIR BAG OFF indicator lamp goes out after the
system self-test. This indicates that the
front-passenger front air bag is activated. If children are traveling in the vehicle, be sure
to observe the notes on "Children in the vehi-
cle" (Y page 61).
When OCS is malfunctioning, the red 0075
restraint system warning lamp in the instru-
ment cluster and the PASSENGER AIR BAG
OFF indicator lamp light up simultaneously.
The front-passenger front air bag is deactiva-
ted in this case and does not deploy during an accident. Have the system checked by quali-
fied technicians as soon as possible. Consult
an authorized Mercedes-Benz Center. The
front-passenger seat should only be repaired at an authorized Mercedes-Benz Center.
If the front-passenger seat, the seat cover orthe seat cushion is damaged, have the nec-
essary repair work carried out at an author-
ized Mercedes-Benz Center.
For safety reasons, Mercedes-Benz recom-
mends that you only use seat accessories
that have been approved by Mercedes-Benz.
If the driver's air bag deploys, this does not
mean that the front-passenger front air bag
will also deploy. The Occupant Classification
System (OCS) categorizes the occupant in the
front-passenger seat. Depending on that
result, the front-passenger front air bag is
either enabled or deactivated.
System self-test G
DANGER
If the PASSENGER AIR BAG OFF indicator
lamp does not light up during the system self- test, then the system is malfunctioning. The
front-passenger front air bag might be trig-
gered unintentionally or might not be trig-
gered at all in the event of an accident with
high deceleration. This poses an increased
risk of injury or even fatal injury.
In this case the front-passenger seat may not be used. Do not install a child restraint system
on the front-passenger seat. Have the Occu-
pant Classification System (OCS) checked
and repaired immediately at a qualified spe-
cialist workshop. Occupant safety
55Safety Z

G
DANGER
If the PASSENGER AIR BAG OFF indicator
lamp remains lit after the system self-test, the front-passenger front air bag is disabled. It willnot be deployed in the event of an accident. In
this case, the front-passenger front air bag
cannot perform its intended protective func-
tion, e.g. when a person is seated in the front- passenger seat.
That person could, for example, come into
contact with the vehicle's interior, especially
if the person is sitting too close to the dash-
board. This poses an increased risk of injury or even fatal injury.
When the front-passenger seat is occupied,
always ensure that:
R the classification of the person in the front-
passenger seat is correct and the front-
passenger front air bag is enabled or disa-
bled in accordance with the person in the
front-passenger seat
R the person is seated properly with a cor-
rectly fastened seatbelt
R the front-passenger seat has been moved
back as far back as possible
If the PASSENGER AIR BAG OFF indicator
lamp remains lit when it should not, the front- passenger seat may not be used. Do not
install a child restraint system on the front-
passenger seat. Have the Occupant Classifi-
cation System (OCS) checked and repaired
immediately at a qualified specialist work-
shop. G
WARNING
Objects between the seat surface and the
child restraint system could affect OCS oper- ation. This could result in the front-passengerair bag not functioning as intended during an
accident. This poses an increased risk of
injury or even fatal injury.
Do not place any objects between the seat
surface and the child restraint system. The
entire base of the child restraint system must
always rest on the seat cushion of the front-
passenger seat. The backrest of the forwards- facing child restraint system must, as far as
possible, be resting on the backrest of the
front-passenger seat. Always comply with the child restraint system manufacturer's instal-
lation instructions.
After the system self-test, the PASSENGER
AIR BAG OFF indicator lamp displays the sta-
tus of the front-passenger front air bag
(Y page 53).
For more information about the OCS, see
"Problems with the Occupant Classification
System" (Y page 57). 56
Occupant safetySafety

Problems with the Occupant Classification System (OCS)
Be sure to observe the notes on "System self-test" (Y
page 55).Problem
Possible causes/consequences and
0050
0050Solutions The PASSENGER AIR
BAG OFF indicator
lamp lights up and
remains lit, even
though the front-
passenger seat is occu-
pied by an adult or a
person of a stature cor-
responding to that of an
adult. The classification of the person on the front-passenger seat is
incorrect.
X Make sure the conditions for a correct classification of the per-
son on the front-passenger seat are met (Y page 53).
X If the PASSENGER AIR BAG OFF indicator lamp remains lit, the
front-passenger seat may not be used.
X Have OCS checked as soon as possible at an authorized
Mercedes-Benz Center. The PASSENGER AIR
BAG OFF indicator
lamp does not light up
and/or does not stay
on.
The front-passenger
seat is:
R unoccupied
R occupied by the
weight of a child up
to 12 months old in a
child restraint sys-
tem OCS is malfunctioning.
X Make sure there is nothing between the seat cushion and the
child seat.
X Make sure that the entire base of the child restraint system rests
on the seat cushion of the front-passenger seat. The backrest of
the forwards-facing child restraint system must, as far as pos-
sible, be resting on the backrest of front-passenger seat. If nec- essary, adjust the position of the front-passenger seat.
X When installing the child restraint system, make sure that the
seat belt is tight. Do not pull the seat belt tight with the front-
passenger seat adjustment. This could result in the seat belt and the child restraint system being pulled too tightly.
X Check the installation of the child restraint system.
Make sure that the head restraint does not apply a load to the
child restraint system. If necessary, adjust the head restraint
accordingly.
X Make sure that no objects are applying additional weight onto
the seat.
X If the PASSENGER AIR BAG OFF indicator lamp remains off, do
not install a child restraint system on the front-passenger seat. It is recommended that you install the restraint system on a
suitable rear seat.
X Have OCS checked as soon as possible at an authorized
Mercedes-Benz Center. Occupant safety
57Safety Z

Deployment of Emergency Tensioning
Devices and air bags
Important safety notes G
WARNING
The air bag parts are hot after an air bag has
been deployed. There is a risk of injury.
Do not touch the air bag parts. Have a
deployed air bag replaced at a qualified spe-
cialist workshop as soon as possible. G
WARNING
A deployed air bag no longer offers any pro-
tection and cannot provide the intended pro-
tection in an accident. There is an increased
risk of injury.
Have the vehicle towed to a qualified special- ist workshop in order to have a deployed air
bag replaced.
It is important for your safety and that of any passengers to have deployed air bags
replaced and to have any malfunctioning air
bags repaired. This will help to make sure the
air bags continue to perform their protective
function for the vehicle occupants in the
event of a crash. G
WARNING
Pyrotechnic Emergency Tensioning Devices
that have been deployed are no longer opera- tional and are unable to perform their inten-
ded protective function. This poses an
increased risk of injury or even fatal injury.
Therefore, have pyrotechnic Emergency Ten-
sioning Devices which have been triggered
immediately replaced at a qualified specialist workshop.
An electric motor is used by PRE-SAFE ®
to
trigger the tightening of the seat belt in haz-
ardous situations. This procedure is reversi-
ble.
If the Emergency Tensioning Devices or air
bags are deployed, you will hear a bang and a small amount of powder may also be released. The
0075restraint system warning
lamp will light up.
Only in rare cases will the bang affect your
hearing. The powder released is generally not hazardous to health, it could however cause
short-term breathing difficulties in people
with asthma or other respiratory problems. In
order to prevent breathing difficulties, you
should leave the vehicle as soon as it is safe to
do so, or open the window.
Air bags and pyrotechnic seat belt tensioners
contain perchlorate material, which may
require special handling or environmental
protection measures. Check with your local
government’s disposal guidelines. California
residents, see www.dtsc.ca.gov/
HazardousWaste/Perchlorate/
index.cfm.
Method of operation During the first stage of a collision, the
restraint system control unit evaluates impor-
tant physical data relating to vehicle deceler- ation or acceleration, such as:
R Duration
R Direction
R Intensity
Based on the evaluation of this data, the
restraint system control unit triggers the belt
tensioners in the event of a frontal or rear
collision.
An Emergency Tensioning Device can only be triggered if:
R the ignition is switched on
R the restraint system components are ready
for operation, see “Restraint system warn-
ing lamp” (Y page 45)
R the belt tongue is inserted into the buckle
on the respective front seat
The belt tensioners in the rear compartment
are triggered independently of the lock status
of the seat belts. 58
Occupant safetySafety