SRS Airbag Fault

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Arnie
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Hello,

I am trying to sort out a problem with the airbag / SRS light being on.

It happened after trying to start the car with a low battery.

 

Anyway, I figured it would be a simple issue to reset it. It's a 1996, G300e, and the is a 16-pin diagnostic connector located near the brake-servo in the engine bay. Only pins 1 (Gnd) , 6 (SRS) and 16 (12 v) are populated in the socket.

I tried to use a carsoft clone, with analogue connector to reset the SRS, but it cannot find the airbag control module. I then wired-up an LED with 330ohm series resistor (for 30mA) and parallel switch to try to do a manual diagnosis of the flash-codes, however, the output on pin 6, has hardly enough power to light the LED, although it does indicate 12v with a digital multimeter.

 

So, I figure that I will need some help with this such as a wiring diagram with relevant components,  relays and fuses, and also, where is the SRS control unit located?

 

Thank you

 

 

 

Howard Green
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Re: SRS Airbag Fault

Have a word with Roly he may be able to help you out .

Roly
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Re: SRS Airbag Fault

You will probably need to get a dealer to reset the light for you. I don't know how you can reset it without a proper tool, HHT or the PC DAS system. I used to have a Carsoft laptop and it used to reset the AB module ok on a 38 pin plug.

Reading the code won't tell you much, only that there is a fault, which you already know. If you disconnect the AB from the system it activates the light. It probably registered a low voltage when you were trying to start it an triggered the fault.

I have a diagram which shows the AB control module near the gear level under the low centre console and, obviously, the AB itself is behind the steering wheel. Does your horn still work?

Arnie
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Re: SRS Airbag Fault

Thank you for the replies. The airbag system is on a 16-pin diagnostic connector, which indicates that it is what's called an "analogue" system. Shorting pin 1( Gnd)  to pin 6 should clear the fault, but it doesn't. Additionally, there should be a fault code read-out , as flash-oodles when a light or LED is connected between pins  1 and 6 (eg 3-flashes = steering slip ring fault etc) , but it's a constant 12v - no flashes at all.. and the output on pin 6 is too low to drive an LED, which may indicate some fault with the module.

The steering wheel horn is fine, and I have moved the steering wheel back and forth in case the brushes were sticky.

I therefore  think that somehow the airbag module has failed completely, and I am thinking I will need to replace it. However, first, I need to find where it's located, but I don't know whether there are two modules ( main controller and crash sensor) or just one integrated module. I believe that the crash sensor should be somewhere on the transmission tunnel.

Do you have the wiring diagrams, please? id like to check whether there  may be any relevant fuses or relays to check as well.

 

i see that Mercedes  w124 airbag modules sell for about £10 on eBay, but I need to see which is the correct one.

Thanks

 

 

 

Roly
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Re: SRS Airbag Fault

This is the best I could find. I presume that you have the driver's AB only. Not the later type with passenger and belt tensioners?

Send me a PM with an email address and I'll send you a 2Mb file with all the instructions for the ab retrofit, which has lots of tech info on electrics. Or put it here if you're not worried.

Arnie
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Re: SRS Airbag Fault

Thank you, Roly,

 

That was useful. I'll send you a PM with my email address for the rest. Yes, it's a 300GE with only the driver's airbag.

I spent the afternoon trying to find the airbag module, no no avail.

Roly
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Re: SRS Airbag Fault

Wow , going in deep.

Email sent.

 

Arnie
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Re: SRS Airbag Fault

OK, after some more research, it seems that the Airbag controller should be located between the two gear levers, under the plastic sub-tray. Some more dismantling is required.

Arnie
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Re: SRS Airbag Fault

hello,

 

I now have the airbag module from the car. it appears to be a version fitted to the W202 C-Class during mid-90's. Hence, although it's connected to an 'analogue' style diagnostic port for blink/flash-codes, it may well be digital, so i will try resetting using the digital protocols in Carsoft.

Interestingly, new modules require vehicle coding, which means that the module must be able to communicate digitally in some way through its diagnostics connection.

 

Through google, I have found his comment on another forum:



"...on the w202 c class benzes the srs can come on for 2 reasons on the 97 model. 1 you took the battery off the car or it ran flat with the key in and turned to position 2.. or your pad in the passengers seat has been compromised.. if you haven't got a passenger airbag (that means you will have a really big glove box).. just take your car to a mercedes or german specialist and they should be able to reset the fault and the light will go away.. happened twice one my 97 c180 ..."
 


I think the 1st reason is pretty much what happened to me at the time: the battery died cranking in key-position-2

 



 

 

 

Arnie
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Re: SRS Airbag Fault

I will find out for sure tomorrow, on the car, but it seems that I have found some answer here:

**** { Digital SRS module on an old-style 16-pin analogue diagnostic connector: } *****
**** { Test as analogue first, then digital, on pin 6 (16-pin) or pin 30 (38-pin)  } *****


http://www.motorsforum.com/mercedes/diagnostic-software-srs-airbag-issue-9455-.htm


"....I am currently in the middle of a major dispute with Mercedes-Benz regarding
 diagnostic software and why it is so completely useless with some older
 models, in my case, a UK 1995 E200-124 with an SRS problem.

 During my research which has often led me up a number of 'blind alleys', I
 came across the following extract from a technical bulletin.  To my
 untrained eye, this reads like an explanation of why current MB diagnostic
 software (Star) is unable to obtain the error codes necessary to diagnose
 faults.  I need to know if my assumption is correct.

 Do I also assume that I must have an analogue connector, simply because it
 is 16-pin?  With some helpful assistance, I managed to check this for
 myself; the diagnostic box is located behind the firewall and in front of
 the brake fluid reservoir (on U.S. specs, I understand that it is located in
 front of the battery).

 Incidentally, are U.S. MB dealers legally obliged to follow the procedure
 laid down in this bulletin?

 TC


 Carsoft USA Technical Bulletin ABM: 310803d: COMMON PROBLEMS AND SOLUTIONS
 FOR CARSOFT MB


 5. "Module Does Not Respond"

 Problem:  Is the module digital or analogue?

 Chassis Affected:  1992-1994 W124, W140, R129, and W202


 1.  Between 1993 and 1995 production dates, Mercedes-Benz models had a mix
 of some digital and some analogue modules on the same car.

 2.  Technicians should be aware that these cars might have a 38-Pin digital
 connector, or an 8/16-Pin analogue connector. A 38-Pin Connector does not
 guarantee an all-digital car.

 3.  If in these cases, analogue diagnosis is still required through the
 38-Pin connector or the 8/16-Pin analogue Connector for the analogue
 modules.

 4.  Not all cars are affected.


 Analogue or Digital: Airbag


 1.  All digital from 1994-1995; but finds only one fault at a time, just as
 1988-1993 analogue cars.

 2.  Clear each fault before testing for the next fault.

 3.  Test as analogue first, then digital, on pin 6 (16-pin) or pin 30
 (38-pin)

MTHamill
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Re: SRS Airbag Fault

Hi Arnie,

Re the fault with the SRS in your G300 back in 2004!

The SRS light is staying on constant in my 1994 G300GEL and I was wondering if you needed to change the sensor or just do a reset to clear the fault?

I noticed online the Airbag can be tested using a multimeter maybe this is where I should start?

Any suggestions would be much appreciated.

Martin

 

MTHamill
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Re: SRS Airbag Fault

Just noticed the fault was in 2015.