W168 A Class SRS Airbag Light

Vlad

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Various Mercs come and go
Just posting this as it may be useful when somebody with an A Class does a search in the future due to their SRS/Airbag light coming on.

Problem: The SRS/Airbag light started to show constantly on my wife's A Class (2004 car).

Took it down to my local specialist and they stuck it on the diagnostics and it showed up that there was an open electrical circuit in the airbag system.

On a lot of A Classes the SRS light comes on when a sensor in the passenger seat fails or a contact behind the airbag in the steering wheel fails.

However, this was not the problem on mine....it turned out to be the airbag control unit. This is a smallish box of tricks (about the size of a box of cigarettes) that sits behind the centre console and apparently mine is not the first A Class they have seen with the problem. Only solution was replacement and it had to be a new unit from MB as they are programmed to the individual car, so you can't get them second hand....cost of the new unit a painful £461+vat !!....total cost with vat, fitting +dignostics was something like £660

So if you are buying an A Class with a glowing SRS light make sure you get it checked out.
 

Strat

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Jun 10, 2009
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I had a similar problem on my wifes A160CDI, with ignition off I disconnected connector under passenger seat, checked for poor connections etc, all was fine so, I un-clipped the passenger seat cushion, detatched some clips under seat to release a pair of round metal strips which run fore/aft, these form the shape of the cushion. I positiioned them over the weight sensor film thing, then put it all together which was a bit of a fiddle, reconnected & have had no light problem with it since.
Plenty of other unrelated problems though: rear door rattle, leaking rear screen wash leak flooded central locking pump in boot, blocked screen wash pump & clutch went @ 66K.
 

Studley75

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Nov 13, 2013
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By the sounds of things I'm in for a hefty bill then?
My Y reg W168 A class has the SRS light showing constantly. Diagnostics showed a fault in the drivers side door airbag, but on inspection all was fine. I know there can be issues with the sensor pad on the front passenger seat, but nothing showed up in diagnostics?
I can only assume it's going to be something very pricey & I'm at a loss about where to go for help. Looks like an expensive trip to Mercedes then, unless anyone knows if this problem can be sorted cheaply? Does it need sorting? Can the light not be disconnected if all the air bags are fine & will deploy in an accident? Your thoughts would be greatly appreciated?
 

sbhep

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Nov 25, 2015
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A170 cdi
I have bought a A170 that has been in a bump airbags are fine but seat belts been activated, can I swap this module for another secondhand one or is it new only.....Where is this module located ????? car is only worth £1000 done so not worth worth spending hundreds on .....cheers
 

wongl

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Worth trying a second hand module and getting STAR with developer mode to copy the configuration/code from old module and transfer to second hand module to see if it will work?
 

GLK

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I have bought a A170 that has been in a bump airbags are fine but seat belts been activated, can I swap this module for another secondhand one or is it new only.....Where is this module located ????? car is only worth £1000 done so not worth worth spending hundreds on .....cheers
Have done exactly that on my old (now sold) W168 - bought a reconditioned SRS ECU for about £30, if I remember correctly, and had it fitted by PCS - not a single problem in four years after that.

Again, in I'm not mistaken, the SRS ECU is under the central console, somewhere between the handbrake and the gearstick ... BTW, when the old one was removed, we discovered it was drenched in coffee. At least I hope it was coffee :crazy:

Before you go swapping ECUs, try to see if the fault can be cleared - if as you said, only pretensioners were activated, I think it should be possible?
 

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