Airbag / SRS warning light after replacing seats

"I replaced the seat with a new one and now I'm having an airbag / srs light on. Do you have a device to turn it off?"

This is a problem that customers often contact us with.

For various reasons, the seat can be replaced. Sometimes the old one is destroyed, sometimes instead of a single one we prefer to have a double one (in minivans). It happens that users decide to completely remove one seat to have more space.

What happens when we disconnect the old seat

If we want to take out the old seat, we disconnect various components from the car installation – depending on the car’s equipment, that can be airbags, seat belt pretensioner, seat belt buckle, seat occupancy sensor, seat heating, electric seat control or some module.

What does the car computer see then?

Car’s control units recognize that particular parts have been disconnected. In case of disconnecting elements of the SRS system, the airbag control unit immediately displays an error in the form of an airbag / SRS indicator on the dashboard. Depending on the equipment of the car, the indicator may also appear on the middle screen, and sometimes also on the headliner (mainly in case of BMW from the USA / Canada).

When a particular component is disconnected, it will not work properly. The car installation treats it as an ordinary malfunction.

The SRS system is responsible for safety in the car and any inconsistencies are treated by control units as faults in the operating system.

What happens when we connect the new seat

If the original seat and the new seat are exactly the same and yet after connecting the new seat, the indicator lights up, it should be sufficient to remove the errors using diagnostic software.
In case this is not enough, make sure all parts have been properly connected. When you see nothing visually, computer diagnostics will show which component(s) causes the problem.

However, in most cases the new seat comes from a car with a different year of issue or different version. Sometimes this is the reason for the exchange, that it is somehow different. For this reason, it may have different equipment. In this case, removing fault codes without solving problems with components won’t hel – if the indicator goes off at all, it will most likely come back after a short time.

We explained that when disconnecting the old seat we disconnect the various elements from the car installation. Therefore, when connecting a new seat, all the elements that we disconnected should be connected. Sometimes, however, this is not possible – because the part(s) in the new seat does not occur or is different. In such case, you need to bypass such part(s) because car installation still contisues to demand it – the emulator of the part will help to bypass it.

The bottom of the seat with different connectors - Mercedes S W220

How do you know which components cause a problem?

If, for example, you have two plugins that are not connected to anything, then probably this two plugs make the warning light appear. If you do not know from which parts these plugs come from, it is best to perform computer diagnostics using the appropriate diagnoscope – it will show exactly which elements are causing the problem.

Once we know from diagnostics which elements require attention, and the reason for this is the fact that they are not connected to anything, we can use the emulator of the part that will simulate that the part is connected and works properly.

Solving a problem with the SRS/airbag warning light looks similar in different cars, even though the equipment is different.

Example I - Mercedes Benz

In Mercedes Vito / Viano, after removing the single seat (which is equipped with a seat occupancy sensor) and replacing it with a double seat (which is not equipped with a seat occupancy sensor), we will need a seat occupancy sensor (mat) emulator. After connecting it, you can remove the error of the faulty (in this case not connected) mat.

Is that enough?

Yes, if the seat mat is the only part that causes the light to be displayed.
No, if there are other fault codes in the airbag control unit which come from another components.
For example: if computer diagnostics also shows the seat belt tensioner fault code, then connecting only mat emulator is not enough – it will eliminate the problem of the seat mat, but the problem with the seat belt tensioner will remain. There is also a seat belt tensioner emulator – if for any reason we do not have a place to connect the plug from the tensioner, we can use the emulator. In this way, we repair / connect / replace / bypass any component that causes an error in the airbag control unit. Finally, we reset fault codes using the appropriate diagnostic software. Thanks to this, the control unit will receive relevant information from each component and stop displaying the light.

Example II - BMW

Another common and one of the more difficult examples is BMW E60, let’s assume the car is pre-facelift, with a metal key. The front passenger seat is replaced – the new seat, however, comes from the E60 facelift version. The seat occupancy sensors in the pre-facelift and facelift versions are different, so it will not be possible to connect the seat mat from the new seat to the installation of the car. It differs not only with the plug, but also with electronics.

Which emulator to choose – the one for the pre-facelift version or the one for the facelift?

The emulator must be connected to the car installation, not to the seat – it must be compatible with car installation then. Therefore, we need an emulator for the seat mat which was originally in the car – in this case the pre-facelift version.

Is the seat mat the only problem in this E60?
The answer is similar to the previous case. It depends on which elements were disconnected when removing the seat but were not connected to the installation after inserting a new seat. The seat mat is just one of the components. There are, among others, airbags, seat belt tensioner, seat belt buckle. If we are not sure – the easiest way is to perform computer diagnostics.

Replacing the seats does not always have to be troublesome. 
It is worth to carefully analyze all connectors.

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