Supplemental Restraint System (SRS) (Mercedes-Benz M-Class W163)

The devices and components that make up the supplemental safety system (SRS) include:

• Two front ones (frontal) airbags. The driver's airbag module is housed in the steering wheel hub. The front passenger airbag is housed in a special cavity on the right side of the vehicle's instrument panel. The locations of both airbags are marked with warning signs "SRS AIRBAG";
• Four side airbags for the front and rear seats. The side airbag modules are mounted in the corresponding doors of the vehicle;
• Head airbags (curtain airbags) located along the side edges of the ceiling panel and providing additional protection for the heads of the driver and all passengers in the event of side impacts and vehicle rollovers;
• Directional G-sensors that are triggered in the event of a severe frontal/side impact;
• Electronic self-diagnostic system, which, when the ignition is on, provides continuous testing of overload sensors, control unit, airbag gas generators and connecting electrical wiring of the corresponding circuits;
• Automatic emergency seat belt tensioners built into the front seat belt retractors;
• SRS malfunction indicator lamp mounted in the instrument panel;
• A spare, autonomous power source designed to duplicate the main power system in the event of its failure during a collision.

A special SRS warning lamp is mounted in the vehicle's instrument panel (see Section Instrument cluster, gauges and control lamps and indicator lights), designed to warn the driver about failures in the additional safety system detected by the self-diagnostic system. Depending on the vehicle configuration, the activation of the warning lamp indicates possible malfunctions of the front/side airbag modules or automatic emergency seat belt tensioners.

Operating principle of frontal airbags

Warning! Never transport young children in the front seat of a vehicle equipped with a passenger airbag! This also applies to installing a special child seat in the front seat.

Note: In minor collisions and rollovers, the front airbags should not deploy.

The front airbag modules are mounted in the steering wheel hub and in the right-hand side of the instrument panel, directly above the main storage compartment.



The driver's front airbag module (1) is mounted in the steering wheel hub (the decorative cover is marked accordingly).



The front passenger airbag module (2) is mounted on the right side of the instrument panel (the decorative cover is marked accordingly).



Directional overload sensors react to the excess of a certain limit value, which may occur during a strong frontal collision. At the signal from the sensors, the control unit turns on the airbag gas generators, causing their immediate filling.

During a collision, the seat belt keeps the lower part of the occupant's body from moving. Front airbags help prevent injury to the driver and front passenger when their heads and chests hit the steering wheel/dashboard.



Airbags deploy immediately at the moment of collision; immediately after deployment, the gas from the airbags is released, which allows the driver to maintain adequate visibility.

Since the signals for both airbags to operate come from the same sensors, both airbags operate simultaneously. However, it is possible that only one of the airbags will be activated. This becomes possible when the magnitude of the directional overloads that arose during the collision was at the limit of the sensitivity range of the sensors. In this case, the seat belts provide sufficiently reliable protection for the driver and front passenger, while the effect of the airbag operation will be minimal.



Immediately after the airbags are triggered and perform their functions, the gas is released from them, which allows the driver to maintain visibility and freely manipulate all vehicle controls.

The entire duration of the process from the moment the overload sensors send a signal to the release of gas from the airbags takes a fraction of a second. The airbags are triggered so quickly that the human ear is simply unable to perceive the pop of the gas generators when filling the airbags.

After a traffic accident in which the airbags were deployed, the interior of the car looks slightly smoky. In fact, this is a suspension of fine powder, which is usually sprinkled on the folded airbag shells. People with respiratory diseases may experience some discomfort from the gaseous products contained in the air, emitted by the airbag gas generators.

Operating principle of side and head airbags

The side airbag modules are mounted in the side door panels of the vehicle. The locations of both side airbags are usually marked with inscriptions "SIDE AIRBAG".



The front side airbag modules (3) are mounted in the front door panels of the vehicle directly above the armrests.





The rear side airbag modules (4) are mounted in the rear door panels of the vehicle directly above the armrests.

The head airbag gas generators are located along the side edges of the ceiling panel.



The head airbag gas generators are located along the side edges of the ceiling panel.

In the event of a severe side impact, the directional overload sensors record the excess of a certain threshold value by the loads that arise and send an information signal to the control unit, which generates a command to trigger the gas generator of the corresponding side airbag. In this case, if the impact occurs from the passenger seat, the corresponding side airbag will trigger even if there is no passenger in the seat.





Side airbag deployment diagram (the airbag deflates immediately after activation).

To ensure that the airbags provide the most effective protection, the driver and passenger sitting in the front seat should sit up straight and be wearing seat belts.

SRS Malfunction Indicator Lamp Operation Procedure

When the ignition is turned on (the ignition key is turned to position 2) the control lamp lights up for a short time and then immediately goes out, which confirms that all system components are functioning properly.

If the warning light comes on at any other time, the vehicle owner should contact a Mercedes-Benz service station for help as soon as possible. Such situations include the following:

• The indicator lamp does not turn on when the ignition key is turned to position 2;
• The indicator lamp remains on after the engine has been started;
• The indicator lamp is activated and lights up in a constant or flashing mode while the vehicle is moving.

If the above symptoms of malfunction are present, the additional safety system may fail in the event of a vehicle accident.

Warning! Ignoring the SRS warning light signals can lead to the most serious consequences if the airbags fail during a traffic accident!

Seat belts with automatic emergency tensioners

The return devices of the three-anchor seat belts of the front seats and the side seats of the second row rear seat are equipped with emergency automatic tensioners. The tensioners are activated by strong frontal overloads that occur during a frontal collision and provide instant selection of slack in the belts, as a result of which the straps of the latter tightly encircle the body of the occupant, significantly increasing the level of protection for the driver and front passenger.

The tensioner (A) is mounted in the belt return mechanism assembly. The procedure for using such seat belts is similar to the procedure for using conventional belts equipped with inertial return devices. The tensioner operation mechanism is absolutely transparent to the user and does not require any additional skills or knowledge from the latter.



The tensioners are activated only under significant frontal overloads. The activation of the modules is accompanied by a loud bang and a small amount of smoke.

Note: The smoke released when the tensioners are triggered is safe for human health, but when inhaled directly it can cause irritation of the mucous membranes.

It should be noted that failures of tensioners to operate during a frontal collision in most cases are explained not by a malfunction of the system, but by the fact that the overloads that occur during the impact do not reach the threshold value at which the modules are activated.

As with airbags, the emergency tensioner modules are designed for a single deployment and after that are subject to replacement together with the belts - contact the Mercedes-Benz service stations. All claims regarding failures of SRS components are also accepted there.

Maintenance of SRS components

Airbags and automatic emergency seat belt tensioners require virtually no regular inspection or maintenance. However, the owner of a suitably equipped vehicle should keep the following points in mind:

• After the airbags have been deployed, they must be replaced along with the system control unit. Do not attempt to remove the airbags yourself. These operations must only be performed in a car service workshop;
• If the SRS warning light comes on and indicates a system failure, you should immediately contact your nearest Mercedes-Benz service station for a full diagnosis and any necessary repairs to the system. Otherwise, the airbags may not deploy in an accident and may not perform their protective function;
• Only specially trained personnel are allowed to work with additional safety system components. It is prohibited to independently dismantle airbags and emergency seat belt tensioners from the vehicle. In the event of SRS failure or after emergency deployment of airbags and seat belt tensioners, it is necessary to contact a Mercedes-Benz service station for repair or replacement of system components;
• Do not open modules or modify the wiring of the airbag systems and automatic emergency seat belt tensioners - such intervention may lead to inadvertent deployment of the airbags and tensioners and cause injury to the operator or nearby people;
• Do not replace the front seats without first consulting a Mercedes-Benz service station. Careless or incorrect replacement or removal of the covers may result in the failure of the side airbags to deploy in the event of an accident.

When transferring the vehicle to another person, it is mandatory to inform the latter about all installed SRS elements, indicating the relevant points in the vehicle operating instructions.

On all models equipped with SRS, special warning signs are installed in places where the active elements of the system are located.