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How to check if the seat mat is 3-wired in Mercedes A W176, B W246, C W204, ML W166 and some others?

The seat occupancy sensor in most new Mercedes models may have 2, 3 or 4 wires:

  • white, red, brown (3-wired mat)
  • blue, brown, black (3-wired mat)
  • black, black (2-wired mat)
  • white, red, brown, green (4-wired mat in some models with WSS system, although wires colors may be different in case of the 4-wired seat mat)
Below there are photos of the versions. The photos were taken under passenger side seat.

3-wired seat occupancy sensor
- brown, blue, black:

3-wired seat occupancy sensor
- red, white, brown:

2-wired seat occupancy sensor - black, black:

4-wired seat occupancy sensor - GLA USA

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Restraint System Malfunction – what does it mean?

Due to numerous questions, we explain what to do if the on-board computer shows a message like this…:

or like this…:

or this…:

or this…:

or when the airbag / SRS warning light on the dashboard appears:

This means that one or more components that make up the SRS passive safety system have failed.

In all cases shown in the pictures above, computer diagnostics should be performed in order to find out what exactly is damaged in a car.
A good diagnostic computer will display codes with descriptions explaining which components of the safety system need to be fixed.

The information from the above pictures does not inform what exactly is damaged. You will find out about this from computer diagnostics.

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Mat emulator for BMW 7 Series E65 E66 – which one to choose?

The warning light popped out, computer diagnostics showed faulty seat occupancy sensor. A decision was made to buy the emulator.
But… which one to choose as there are several versions?

EU / US

It should be determined whether the car was manufactured for the European market or for the American market. This is important information because such cars differ in equipment and have different seat occupancy sensors.

Emulator for the driver's or passenger's seat?

BMW 7 E65 is the only BMW model in which the seat mat appears not only in the passenger side seat, but also in the driver side seat and the rear seat. So you should find out which exactly seat occupancy sensor is faulty. Good computer diagnostics will show you such information.

Emulator for passenger side seat - information

Seat mat emulator

There are two types of the seat occupancy sensor on passenger side seat on E65/E66:

– 2-wired mat (2 pin mat connector) is usually placed on E65 up to 2004/5 EU version and up to 2003 US version

– 3-wired mat (4 pin mat connector) is usually placed in models manufactured after 2005 (EU versions) and after 2003 (US versions).

To be sure about the type, please check the plug under the seat (photos of both versions are placed at the bottom of the site, below the article).

Seat belt buckle emulator

After fitting the seat occupancy sensor emulator, a car computer sees the seat as always occupied and asks to fasten seat belt – even if there’s no one sitting in the seat.

The solution for not driving with seat belt always fastened is connecting the seat belt emulator which turns off the seat belt warning light / sound.

Emulator for driver side seat - information

Seat mat emulator

There is usually 2 wired seat occupancy sensor (2 pin mat connector) on driver side seat but to be 100% sure, please check the plug under the seat.

Seat belt buckle emulator

We assume that a driver always fastens the seat belt, so in case of the driver’s seat, the seat belt emulator is not needed.

Pictures of the connector - 2 pin, 2-wired mat

2 pin mat connector has wires: blue, white

Pictures of the connector - 4 pin, 3-wired mat

4 pin mat connector has 3 wires: brown, red, white
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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 continues 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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Mat emulator for BMW 5 Series E60 E61 and 6 Series E63 E64 – which one to choose?

The warning light popped out, computer diagnostics showed faulty seat occupancy sensor. A decision was made to buy the emulator.
But… which one to choose as there are several versions?

In BMW 5 Series E60 E61 and BMW 6 Series E63 E64, the seat mat types are the same and the choice of the emulator looks the same, which is why both models will be described in one article. At the same time, we note that the article below applies to these models only.

Emulator for the driver's or passenger's seat?

At the beginning it is worth realizing one thing.
In W211, the seat mat is placed on the passenger side seat only. There is no seat occupancy sensor on the driver side seat, therefore you will not install an emulator there.

EU / US

It should be determined whether the car was manufactured for the European market or for the American market. This is important information because such cars differ in equipment and have different seat mats.

2-wired seat occupancy sensor

2-wired mat (2 pin mat connector) was usually placed in models manufactured before 2005 (European versions) and before 2003 (US versions).

European cars equipped with a two-wired mat usually have a metal key (not electronic). Thanks to this, we do not have to check if the mat has 2 wires. Let’s just remember that this simplification works if no changes have been made to the car’s installation, no seats have been changed. To be 100% sure, that would be best if you could check under the passenger seat if the seat mat has 2 wires.

In American cars, it is not possible to recognize the type of mat basing on the type of the key – here you always should check the seat mat type by looking under the passenger seat.

The 2 pin mat connector is located on the back of the seat. It is most convenient to move the seat forward and lift the back of the seat as much as possible. You have to enter the car through the back door. Under the seat there is a black can. On one side, a blue plug with 3 wires is connected. On the other, there are 2 wires (blue, white) leading to the mat plug.

2-wired mat, wires: white, blue. On the left you can see the seat mat emulator and seat belt emulator matching this version. It is important whether the car is European or American.
2-wired mat - seat mat plug is disconnected

3-wired seat occupancy sensor

3-wired mat (4-pin mat connector – one hole in the plug is empty) was usually placed in models manufactured after 2005 (EU versions) and after 2003 (US versions).

European cars equipped with a three-wired mat usually have an electronic car key (engine started with a button). The same as in the previous case, if we have an electronic key, it can be assumed that the mat has 3 wires provided that no changes were made to the car’s installation, the seats were not replaced. To be 100% sure, that would be best if you could check under the passenger seat if the seat mat has 3 wires.

In American cars, check under the seat if the mat has 2 or 3 wires. As mentioned earlier, it is not possible to recognize the type of mat by the type of the key.

3-wired mat, wires: brown, red, white
Pictures of the 4-pin mat plug (3-wired mat). The plug is located under the seat, between the center and the back of the seat.

To sum up: in order to buy the correct emulator that fits your car, you need to know two things:
1. whether the car has been manufactured for the European or American market
2. whether the seat occupancy sensor has 2 or 3 wires.

All versions can be purchased in our online store or, if you’re still not sure about the correct version, you can contact us.

Why is there the seat belt buckle emulator?
Is it needed or is the seat mat emulator enough?

As a result of installing the seat occupancy sensor emulator, the car computer “sees” the passenger seat as always occupied (even if there’s no-one sitting in the seat). Therefore, in car models equipped with the unfastened seat belt warning system, the unfastened seat belt warning light or/and sound will appear – the seat belt emulator sends to a car computer information that the seat belt is fastened and switches off the unfastened seat belt warning.

All E60/E61 and E63/E64 are equipped with such system, that’s why the seat belt emulator is needed.

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Mat emulator for Mercedes E Class W211 – which one to choose?

The warning light popped out, computer diagnostics showed faulty seat occupancy sensor. A decision was made to buy the emulator.
But… which one to choose as there are several versions?

Emulator for the driver's or passenger's seat?

At the beginning it is worth realizing one thing.
In W211, the seat mat is placed on the passenger side seat only. There is no seat occupancy sensor on the driver side seat, therefore you will not install an emulator there.

2-wired or 3-wired or 4-wired seat mat?

In any case, check if the seat occupancy sensor has 2 or 3 wires. The seat mat connector is placed under the passenger seat.

Mat is 3-wired - what next?

An emulator without a plug will fit into all W211 with a three-wired seat mat. It is ended with pins (terminals). The assembly is not easy. Remove the mat wires from the original mat plug under the seat (using, for example, a small screwdriver), and then insert the emulator wires in the same color order into the plug.

However, if you prefer easier installation, we also offer emulators with plugs. More information below.

3 pin mat connector

W211 produced in 2002 and some models from 2003 have a 3-pin mat connector.

In W211 from 2003 there may be both versions of the plug – 3 pin or 4 pin. For this reason, before buying the emulator, check under the passenger seat which mat plug you have.

3 pin mat connector, 3-wired seat mat

In the picture above, we showed the seat mat plug – in the car the left and right parts are joined together. Please note if the plug in your car has exactly the same shape.

On the left – seat belt buckle connector and seat mat connector from the side of connecting emulators (female plugs).
On the right – the car installation side – male plugs and other colors of wires.

3 pin mat plug - the view in a car

4 pin mat connector

In W211 produced in 2004-2009 and some models from 2003 there is a 4-pin mat plug.

The mat has 3 wires: white red, brown.

4 pin mat connector, 3 wired seat mat

In the picture above, the connector of this version is presented. The photo was taken under the passenger seat, but from the back of the seat. From the front of the seat (car installation side) the wires colors are different.

The first plug on the left is the seat mat plug. One hole in this plug is empty. The first on the right – seat belt buckle plug (wires: yellow, blue).

2-wired seat occupancy sensor

If the seat mat in your car has 2 wires, we can not offer any emulator for this version. However, such mats are quite rare, and their fault is difficult to diagnose.

4-wired seat occupancy sensor

The seat occupancy sensor that has 4 wires can occur in W211 manufactured for the US market in 2006-09.
If you need the emulator for this version, please contact us or check if it is available HERE.

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Mat emulator for Mercedes C Class W203 – which one to choose?

The warning light popped out, computer diagnostics showed faulty seat occupancy sensor. A decision was made to buy the emulator.
But… which one to choose as there are several versions?

Emulator for the driver's or passenger's seat?

At the beginning it is worth realizing one thing.
In W203, the seat mat is placed in the passenger side seat only. There is no seat occupancy sensor in the driver side seat, therefore you will not install an emulator there.

In the models produced in 2004 and 2005 (sporadically also 2006) there may be two types of the seat mat. Before buying an emulator, check under the passenger seat which plug type you have to make sure which emulator will fit.

3 pin mat connector

3-pin mat plug is placed in W203 produced in the years 2000-2004/5, rarely also 2006.
It is especially important to check which plug is under the seat in case of W203 produced in 2004-2006.

3 pin mat plug and 2 pin seat belt buckle plug

In the picture above, we showed the seat mat plug – in the car the left and right parts are joined together. Please note if the plug in your car has exactly the same shape.

On the left – seat belt buckle connector and seat mat connector from the side of connecting emulators (female plugs).
On the right – the car installation side – male plugs and other colors of wires.

3 pin mat plug - the view in a car

4 pin mat connector

In models manufactured in 2004/5 – 2007 there is a 4-pin mat plug.
3 wires inside the plug – white, red, brown. One hole in the plug is empty. Pictures below.

4 pin mat connector
4 pin mat plug - the view in a car

Note that the 4-pin plug also has three wires inside. It’s called 4 pin, because there are 4 holes in the plug – one of them is empty, without a wire.

In both versions of the plug the mat wires have the colors: white, red, brown.

2-wired seat occupancy sensor

If the seat mat has 2 wires in your car, we can not offer an emulator for this version. Such mats, however, are very rare, and their fault is difficult to diagnose.

4-wired seat occupancy sensor

The seat occupancy sensor that has 4 wires can occur in W203 manufactured for the US market after 2005. If you need an emulator for this version, please contact us.

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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.