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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4215
Experience:  Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
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I have a 1996 500 SL SRS light stays..diagnostic..harness..connector

Customer Question

I have a 1996 500 SL

SRS light stays on, dealer diagnostic show it is in seat belts.
I've check harness, wiring looks OK, I replaced latch which has connector to multi box connector on floor below seat, but light still on. Is there a way I can further isolate where problem can be. Can I jump connection to see if light will go off, if so how?
Submitted: 3 years ago.
Category: Mercedes
Expert:  MB Paul replied 3 years ago.
Chat Conversation Started
MB Paul :

Hi, Jumping the connector will just result in the ECU detecting a dead short in the system so this would still put a fault in the system. The resistance for the seatbelt should be around 2-5Ω. You could check the resistance through the seatbelt but this is only advisable with a professional qualitly meter as cheaper ones can actually trigger the seatbelt tensioner when checking the resistance - not good!



 




Another good alternative is to simulate a resistance across the seatbelt connector so the SRS ECU thinks the seatbelt is ok - we use a simulator to connect up & to select any resistance we choose. A cheaper alternative would be to get a 3 or 4 Ω resistor from an electronics shop to put across the connector with the seatbelt disconnected.



MB Paul :

However please be aware that the SRS light will stay on until the faults are cleared with a diagnostic tool, it will not go out just by curing the fault!

MB Paul :

Best regards, Paul

Customer :

Would replacing the actual belt on seat be advisable? Belt does not retract properly in seat. I have already replaced latch.

Customer :

Where is the resistance measured, on main connected below seat or on belt itself?

Expert:  MB Paul replied 3 years ago.
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Expert:  MB Paul replied 3 years ago.
Hi, If the fault codes are with the seatbelt itself then it would be with the emergency tensioner retractors (ETR) built into the seatbelt itself.

This should be indicated on the fault code as R12/1 for the left side & R12/2 for the right side ETR's

Correct diagnosis should be carried out as per the tests mentioned previously before any component is replaced!

The connector is on the side of the seatbelt itself.

Best regards, Paul
Customer: replied 3 years ago.
Does the retractable belt have a connection to the multi connector on floor? I only noticed latch have a wire connector that is connected to main or am I missing something here
Expert:  MB Paul replied 3 years ago.
Hi,

Could you post your VIN number so I can check some details - I cant think from memory if the wire goes straight up the seat back or through a multi connector.

Do you know the codes that were stored?

Best regards, Paul
Customer: replied 3 years ago.
correct year is 1995 Mercedez 500SL Roadster Vin# XXXXX
here is info you requested,
thanks for your assisatance
Expert:  MB Paul replied 3 years ago.
Hi,

Thanks for that - sadly Mercedes has not put any wiring diagrams for your vehicle in their information system but looking at the diagrams for the installation I would imagine it must go through a separation point under the seat base. I could try to confirm this tomorrow when I am back at work to look at the hard copies of the wiring diagrams.

The seat base can be removed to inspect any wiring - there is a screw either side of the seatbase to remove the base. The wiring can then be accessed easily.

Best regards, Paul
Customer: replied 3 years ago.
I've removed the drivers seat several times already and disconnected all connectors leading to floor. I know I've disconnected one coming from latch, Are you saying there should be a separate connector for retractable part? do you think the other wiring contact can be with other controling seat movement? How can I tell which is connector for belt portion.
Can you explain how I can cross over connection with 3 or 4 resistor?
Customer: replied 3 years ago.
Is the retractable part of belt electronic or is it just spring loaded?
I forgot to ask, are the codes you mentioned isolated to driver seat?
Expert:  MB Paul replied 3 years ago.
Hi,

Yes - there should be a wire that runs up the seat back to the seatbelt reel for the ETR's
I would usually disconnect this connector & put a resistor across the 2 terminals to simulate the correct resistance for the SRS control unit.

Before you go stripping the seat out however do you have the codes that were stored? Is it relating to just one or both seats?

Best regards, Paul
Expert:  MB Paul replied 3 years ago.
Hi,

There is a tensioner on each seatbelt for the front seats. They are pyrotechnic charges to fire the tensioner in an accident (similar to what fires an airbag).

Best regards, Paul
Customer: replied 3 years ago.
The connector you mention to cross, do you mean on belt itself or on floor connection.
Is it just a two prong connection?
Expert:  MB Paul replied 3 years ago.

Hi,

 

I would first put the resistor at the connector on the belt itself - this would then rule out the complete circuit back to the SRS control unit & confirm the fault is in the seatbelt if the fault is cleared & the SRS light goes out.

 

Did you ever find out the codes that were stored?

 

Best regards, Paul

Customer: replied 3 years ago.
I've looked for the codes but can not locate at this time. the driver seat is a used seat and suspect may be the problem area
Customer: replied 3 years ago.
I forgot to ask,
You said to cross connector on belt. should the connection to the main floor connection stay connected? is there a connector plug on belt? if so where is that connector located on belt, toward upper area where it feeds in?
also, should the latch side stay connected tofloor connector.
and I believe you said don't clip belt to latch correct?
Expert:  MB Paul replied 3 years ago.

Hi,

 

The connector for the ETR is shown just below the seatbelt reel in the side of the ETR - it looks like a long cylinder on the bottom of the reel.

 

All other connectors should remain connected so the SRS control unit see's a complete circuit.

 

Dont forget the fault codes will need to be cleared before the SRS light will go out.

 

Best regards, Paul

Customer: replied 3 years ago.
I'm assuming I will have enough wiring harness to keep everything connected or should I remove belt entirely from seat? Can I clear codes some way or do I I need to take in to have done?
Expert:  MB Paul replied 3 years ago.

Hi,

 

Once you have access to the seatbelt you should have enough room to test it in situ.

 

There is no way of clearing the codes other than with a diagnostic tool I'm afraid.

 

Best regards, Paul

Customer: replied 3 years ago.
Well, I'll take apart this weekend to see if I can isolate problem, but it's sounds like I can't tell if it works out because light will continue to stay on untill codes are reset, Correct
Expert:  MB Paul replied 3 years ago.

Hi,

 

That is correct - if it is the ETR then with the correct resistance through the connector the light should go out once the codes are cleared.

 

This is assuming this is what the code relates to!

 

Best regards, Paul

MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4215
Experience: Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
MB Paul and 8 other Mercedes Specialists are ready to help you
Customer: replied 3 years ago.
Thanks, I'll give it try
Expert:  MB Paul replied 3 years ago.

No problem, Let me know how you get on.

 

Best regards, Paul

Customer: replied 3 years ago.
Thanks for your assistance
Expert:  MB Paul replied 3 years ago.

No problem at all. Glad to help!

 

Best regards, Paul

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