Why is the SRS/airbag​ warning lit on the dashboard?

... and how to remove it?

If the SRS / airbag warning is on, it means that one or more components of the SRS system have failed.

The airbag system is controlled by itself – it checks the operation of all components of the system as soon as the ignition is switched on. The warning light comes on and goes out after about 4-6 seconds.
If the light does not go out, it indicates a malfunction in the safety system. It is then necessary to check the SRS system (e.g. in a service station) using a suitable diagnostic software.

For what? Isn't it easier to replace something right away?

Without good computer diagnostics, you don’t know which exactly elements of the SRS system are damaged and cause the warning light. And there are really many of such components which may cause the problem. Replacing or repairing various elements intuitively without carrying out diagnostics is the worst idea – it usually ends not only with the release of a fortune, the exchange of elements that work correctly, but also with the lack of knowledge of the construction and operation of the system may cause additional defects. Remember that sometimes the warning light can appear due to even the disconnection of one of the wires or contact impurities.

Click on the photo to enlarge
Click on the photo to enlarge

The picture on the left shows the airbag light “Passenger restraint system”. The picture on the right – message displayed on the on-board computer. None of the pictures shows what exactly is damaged in the car.
So what do the pictures show?
The information displayed both on the dashboard (in the form of a light) and on the on-board computer (in the form of a short message) only tell us that there is a fault in the SRS system – one or more components have failed. They do not say exactly what these components are and what is wrong with them.

SRS (additional passive safety system) consists of three groups:
• impact sensors
• airbag control unit
• actuators – including airbags, seat belt pretensioners, seat occupancy sensor, communication and automatic accident notification systems, battery disconnection systems.

To enable easier identification of the faults, in some cars the way of the warning light flashing has been programmed in the diagnostic module. For example, in many Mazda models, you can see that the light is flashing in a certain cycle. Flashing cycle 47 or 48 (4 flashes – break – 7 flashes) means a damaged seat occupancy sensor (mat) or a fault in the connection between the seat mat and the airbag control unit. However, it should be remembered that the boards decoding such a sign code are not identical for all types and models of cars, even the same manufacturer. In newer cars such solutions are no longer used.

After years of experience in the repair of safety systems, we state that Mercedes are one of the most difficult to diagnose cars. Cheap scanners usually do not give advice (they may incorrectly indicate damaged elements), it is worth going to a mechanic with a good diagnoscope, such as Star Diagnosis. Also the knowledge of the mechanic is not without significance – an unqualified mechanic using professional software can misdiagnose the error.

Some cars "hint" where to look for a fault.
Translation to English: "Malfunction in front of the right side, go to workshop"
The picture comes from a Mercedes E-Class W213.

It would seem that some things you can check yourself – even connections, plugs, wiring harnesses. If you decide to tinker with airbags, remember to disconnect the battery – even the smallest short circuit can activate the gas cushion and, consequently, seriously damage the body. It should also be remembered that improper handling with the car installation can lead to major faults. Often customers complained that when disconnecting the battery or disconnecting the connectors such components as battery safety terminal or airbag control unit were damaged or airbag control unit coding changed. Therefore, it is worth to leave repairing the SRS system to a qualified person.

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