SRS what is it in the car? – Definition and principle of operation

Sometimes drivers complain that for no reason at all, the SRS indicator on the dashboard lights up. This is especially true for owners of used cars purchased abroad. In such situations, experts are advised to check for airbags or see if the contacts connected to this indicator go off.

SRS - definition and principle of operation

Indeed, the SRS is a passive safety system, which is responsible for the state of all elements that provide protection in case of emergency.

SRS (Supplementary Restraint System) is a rather complex system that combines:

• front and side airbags;
• control modules;
• various sensors that track the position of people in the cabin;
• acceleration sensors;
• seat belt pretensioners;
• active head restraints;
• SRS module.

You can also add power supplies, connecting cables, data connectors, etc. to this.

That is, in simple terms, all these sensors collect information about the movement of the car, about its speed or acceleration, about its position in space, about the position of the seat backs, belts.

If an emergency occurs, such as a car collides with an obstacle at a speed of over 50 km / h, inertial sensors close the electrical circuit leading to the airbag igniters, and they open.

The airbag is inflated thanks to dry gas capsules, which are located in the gas generator. Under the influence of an electric impulse, the capsules melt, the gas quickly fills the pillow and it shoots at a speed of 200-300 km / h and is immediately blown off to a certain volume. If the passenger is not wearing a seat belt, an impact of such force can cause serious injury, so separate sensors register whether a person is wearing a seat belt or not.

The seat belt pretensioners also receive a signal and tighten the belt more to keep the person in place. Active head restraints move to prevent occupants and the driver from whiplash neck injuries.

SRS also contacts the central lock, that is, if the doors are locked at the time of the accident, a signal is given to the central locking system and the doors are automatically unlocked so that rescuers can easily reach the victims.

It is clear that the system is set up in such a way that all security measures work only in emergency appropriate situations.

SRS does not activate squibs:

• when colliding with soft objects - snowdrifts, bushes;
• in a rear impact - in this situation, active head restraints are activated;
• in side collisions (if there are no side airbags).

If you have a modern car equipped with an SRS system, then the sensors will respond to unfastened seat belts or improperly adjusted seat backs and head restraints.

Arrangement of elements

As we wrote above, the passive safety system includes many elements that are located both in the engine compartment and in the seats or are mounted in the front dashboard.

Directly behind the grille is the front directional g-force sensor. It works on the principle of a pendulum - if the speed of the pendulum and its position change sharply as a result of a collision, an electrical circuit closes and a signal is sent through the wires to the SRS module.

The module itself is located in front of the tunnel channel and wires from all other elements go to it:

• airbag modules;
• seat back position sensors;
• belt tensioners, etc.

Even if we just look at the driver's seat, we will see in it:

• driver's side airbag module;
• SRS contact connectors, usually they and the wiring itself are indicated in yellow;
• modules for belt pretensioners and the squibs themselves (they are arranged according to the principle of a piston, which is set in motion and compresses the belt more strongly in case of danger;
• pressure sensor and back position sensor.

It is clear that such complex systems are only in fairly expensive cars, while budget SUVs and sedans are equipped only with airbags for the front row, and even then not always.

operating rules

For this whole system to work flawlessly, you need to follow simple rules.

First of all, you need to remember that airbags are disposable, and they must be completely replaced along with squibs after deployment.

Secondly, the SRS system does not require frequent maintenance, but it is necessary to carry out its full diagnostics at least once every 9-10 years.

Thirdly, all sensors and elements must not be subjected to overheating above 90 degrees. None of the normal drivers will warm them up on purpose, but in the summer the surfaces of a car left in the sun can get very hot, especially the front panel. Therefore, it is not recommended to leave the car in the sun, look for a shade, also use screens on the front glass to avoid overheating of the dashboard.

You also need to remember that the effectiveness of the passive safety system depends on the correct position of the driver and passengers in the cabin.

We advise you to adjust the seat back so that its angle of inclination is no more than 25 degrees.

You can’t move the chair too close to the Airbags - follow the rules for adjusting the seats, which we recently wrote about on our autoportal Vodi.su.

In vehicles with SRS, it is necessary to wear seat belts, because in the event of a frontal collision, very serious consequences can be due to hitting the airbag. The belt will hold your body, which, by inertia, tends to continue moving forward at high speed.

Places of possible deployment of airbags must be free from foreign objects. Mounts for mobile phones, registrars, navigators or radar detectors should be placed so that they cannot prevent the pillows from opening. It will also not be very pleasant if your smartphone or navigator is thrown by a pillow in the face of a side or rear passenger - there have been such cases, and more than once.

If the car has not only front airbags, but also side airbags, then the space between the door and the seat must be free. Seat covers are not permitted. You can not rely on the pillows with force, the same applies to the steering wheel.

If it happened that the airbag fired by itself - this may happen due to an error in the operation of the sensors or due to overheating - you must turn on the emergency gang, pull over to the side of the road, or stay in your lane for a while without turning off the alarms. At the time of the shot, the pillow heats up to 60 degrees, and the squibs - even more, so it is advisable not to touch them for some time.

Since the SRS system has a special power supply that is designed for approximately 20 seconds of battery life, you must wait at least half a minute before proceeding to diagnose the system.

You can independently activate or deactivate the SRS, but it is better to entrust this work to specialists who can check it using a special scanner that reads information directly from the main SRS module.

Video about how the system works.

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