Srs; Srs Warning Lamp; Triggering Of Belt Tensioners, Belt Force Limiters And Airbags - Mercedes-Benz A-Class Series Owner's Manual

Airbags and belt tensioners could fail to
deploy or be triggered in an accident despite
the deceleration force being sufficient to trig-
ger the systems, or could be triggered unin-
tentionally. For this reason, never make any
modifications to the restraint systems.
Therefore, you must not tamper with elec-
tronic components or their software.
SRS (Supplemental Restraint System)
Introduction
SRS reduces the risk of occupants coming
into contact with the vehicle's interior in the
event of an accident. It can also reduce the
effect of the forces to which occupants are
subjected during an accident.
SRS consists of:

+ SRS warning lamp

R
airbags
R
airbag control unit (with crash sensors)
R
belt tensioners for the front seat belts and
R
the outer seat belts in the rear
belt force limiters for the driver's and front-
R
passenger seat
SRS warning lamp
SRS functions are checked regularly when
you switch on the ignition and when the
engine is running. Therefore, malfunctions
can be detected in good time.
The + SRS warning lamp in the instrument
cluster lights up when the ignition is switched
on. It goes out no later than a few seconds
after the engine is started.
G
Risk of injury
If SRS is malfunctioning, individual systems
may be activated unintentionally or may not
be triggered in the event of an accident with
a high rate of vehicle deceleration.
Occupant safety
A malfunction has occurred if:
the + SRS warning lamp does not light
R
up when the ignition is switched on.
the engine is running and the + SRS
R
warning lamp does not go out after a few
seconds.
the engine is running and the + SRS
R
warning lamp lights up again.
In this case, have SRS checked immediately
at a qualified specialist workshop. Mercedes-
Benz recommends that you use a Mercedes-
Benz Service Centre for this purpose.
In particular, work relevant to safety or on
safety-related systems must be carried out at
a qualified specialist workshop.
Triggering of belt tensioners, belt force
limiters and airbags
During the first stage of a collision, the airbag
control unit evaluates important physical
data relating to vehicle deceleration or accel-
eration, such as:
duration
R
direction
R
magnitude
R
Based on the evaluation of this data, the air-
bag control unit pre-emptively triggers the
belt tensioners in the first stage.
If there is an even higher rate of vehicle decel-
eration or acceleration in a longitudinal direc-
tion, the front airbags are also deployed.
Your vehicle has adaptive, two-stage front air-
bags. The airbag control unit evaluates vehi-
cle deceleration or acceleration in the event
of a collision. When the first deployment
threshold is reached, the front airbag is filled
with enough propellant gas to reduce the risk
of injuries. The front airbag is fully deployed
if a second deployment threshold is exceeded
within a few milliseconds.
The belt tensioner and airbag triggering
thresholds are variable and are adapted to the
rate of deceleration or acceleration of the
vehicle. This process is pre-emptive in nature.
33
Z