Passenger airbag squib 2 short circuit - Mercedes Benz SLK Forum

SLK R172 General Discussion Discussion regarding the Mercedes SLK R172

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#1 Old 1 Week Ago
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Passenger airbag squib 2 short circuit

My OBD2 reader and my instrument cluster reports a short circuit somewhere on the wire, for the Passenger airbag squib 2.

The passenger airbag has two squibs, the R12/4 and R12/5, from which a 2 and 2 wire cable comes and connects into the X28/12 plug (4 wires).

The part number of this wiring is A1725406005

When unplugging this wiring from the X28/12 connector, the short circuit error dissappears (but an open circuit error appears, logically).
This leads me to believe that the short circuit occurs between this plug (X28/12) and the airbag.

Now, on the WIS wiring diagram, I see there is a switch on the R12/4 and R12/5.

If I remove the wiring entirely, the multimeter reports no short circuits on it.
But if I plug the wiring to R12/4 and R12/5, both 2 wires for both plugs/squibs report a short circuit on the multimeter.
No error is shown for any short circuits on squib 1, though.

Do you have any idea if this switch is supposed to be open or closed?
Also, do you know how that switch is being actuated?

Some things about the pictures:
1 - I realize there is some spring in this switch (X28/12), which makes a short circuit on the wires for R12/4 and R12/5, when this plug is disconnected. I made sure the spring makes no contact, when checking with the multimeters for other short circuits.
2 - That orange thing must be pushed in, when the squib plug is connected. Perhaps that actuates the switch from the diagram?
3 - What is that? Is it only reinforcement for the wires, so they don't break?

Sorry for being so technical, but I think this can only be explained in technical words.

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#2 Old 1 Week Ago
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As this is a critical safety system it has enhanced fault detection, the switch mentioned is part of that.
Is there a short on the airbag side?
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#3 Old 1 Week Ago
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The Orange tab connector design is to facilitate proper connection easily. If I remember correctly pushing the tab on a disconnected wire will not resolve fault.
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Quote:
Originally Posted by VII7 View Post
As this is a critical safety system it has enhanced fault detection
This means a Star/DAS would be able to tell me the exact wiring which has issues?

Quote:
Originally Posted by VII7 View Post
the switch mentioned is part of that.
So what does this switch do, more specifically?

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Originally Posted by VII7 View Post
Is there a short on the airbag side?
Not sure where the short is, using a generic OBD fault reader, all I get is error code "8011 Short circuit between two wires on passenger side airbag squib 2".

Playing around with the multimeter, and plugging/unplugging the X28/12 connector, it looks like the short is somewhere between wiring AB2 and the internals of the airbag.
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Xentry won't tell you much more.

For diagnosis:
1. Disconnect wire at airbag
2. Test resistance, value should be between 1.8-2.5 ohm

Remember you are working with explosive devices, keep away from the inflation path and keep the inflation path clear, risk of serious injury or death.
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The switch shorts the terminals when the connector is disconnected. If you had an open circuit problem you could use this to diagnose.
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For your car, you need Xentry ( das is for older models ), on xentry you will be able to do further tests.
You can have a cheap Xentry setup, take a look here:
https://www.slkworld.com/das-star-co...ternative.html
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I can help with the installation of DAS/Star Mercedes, XENTRY,EPC, and WIS PM me.
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#8 Old 1 Week Ago
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Quote:
Originally Posted by VII7 View Post
Xentry won't tell you much more.

For diagnosis:
1. Disconnect wire at airbag
2. Test resistance, value should be between 1.8-2.5 ohm

Remember you are working with explosive devices, keep away from the inflation path and keep the inflation path clear, risk of serious injury or death.
Thanks for the resistance range. May just be the problem. Multimeter reports 1.2 Ohm on squib 2. Will look tomorrow into getting a 2.2 Ohm resistor, and if the error code is fixed, then the problem is obvious

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For your car, you need Xentry ( das is for older models ), on xentry you will be able to do further tests.
You can have a cheap Xentry setup, take a look here:
https://www.slkworld.com/das-star-co...ternative.html
THANK YOU THANK YOU THANK YOU!!!
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Got a spare airbag from a 2017 SLC, from Poland, for little over 100 Euros.

Replaced it, and now all is fine.

This is what it takes to replace it:
Remove all the screws from the dash, pull it forward, and then you will have access to the airbag screws, and the airbag has enough space to slide out. (nice engineering ehem)
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#10 Old 6 Hours Ago
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Those switches are called "shorting bars", and if that orange bit isn't fully snapped into position you'll see these "short circuit" messages.
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Quote:
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Those switches are called "shorting bars", and if that orange bit isn't fully snapped into position you'll see these "short circuit" messages.
Haha too little too late. That is exactly the confirmation I was looking for.

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2 - That orange thing must be pushed in, when the squib plug is connected. Perhaps that actuates the switch from the diagram?
When I replaced my dash, to a leather one, I broke part of the plug, because from below, the orange thing wasn't visible/obvious, that it needs to be pulled out (even now, I think you can (comfortably, at least)) only pull the orange thing out, once the airbag is removed from the dash (which requires pulling the dash forward).

The new airbag came with the wiring as well (although UK wiring), so I replaced the plugs on my wiring, with the plugs from the new wiring.

Probably, at this point I have a fully functional airbag in my closet, but I'm currently too lazy (yesterday was enough) to pull the car apart again, and test it with the new wiring/plugs, so at this point, I wish I didn't even know about this information )) (I should have probably done that yesterday, though, didn't cross my mind).

Thanks, though (can't deny, I've learned many things in the process!)
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