Technical Airbag OCS (Oh god! Not another thread!)

[ale199020]

Hi,

now I know this has been discussed over, and over. And over again and I have searched but couldn't find any answer to my particular question. So I rang a dealership and got told to either spend £80 for a diagnostic or go take a hike and get off the phone (admittedly slightly more politely, if only slightly).

So I have the - now widely accpeted as a perk of the Stilo - airbag light and having plugged in multiecuscan have quickly narrowed it down the the OCS. It says that it is recieving an unknown signal from it. So go to the connectors and clean them you say! I have done that, plenty of times, but to no avail. I will admit that I have not tried soldering the wires yet but I will soon.

Now onto point! Hopefully i'll have a OCS coming that I can play with. I'm a big believer in "if it can break it can be fixed" so when it arrives I want to try work out what exactly decides its had enough with these sensors. I also want to try work out what sort of signal it sends to the airbag ECU. From looking at the wiring diagram on eLearn its go three connections (see attachment, K65 is the OCS so far as i'm aware) , 12v +, earth and a line to the ECU. Does anyone have the technical data on what signal it is supposed to send down the line? Does it work in the same way as the airbag on/off switch where it will register a different resistance depending on conditions, i.e resistance a for 50-70kg occupant , resistance b for 70-90 etc (a simplified example), or is it sending some other kind of signal? And, more importantly, whats the best way to measure this? Obvisouly I'll do all my measuring with the OCS out of the car so I can't set off all the internal fireworks!

Also if anyone has a wiring diagram for the OCS it self, or has any other technical data on it that would be much appriciated.

Finally - if you're still reading you deserver a pint -at some point after all this messing I will probabaly want to play with it while its connected to the system. "Noooo!" i hear you cry! But fear not, my plan is to go round and disconnect all the actual air bags so that they can't be set off. My question is, if all the airbags are unplugged I assume the system will pull up an error for every airbag missing and thus shut down and won't try to fire. But what will happen when I finish and plug it all back in? If we say my process will be as follows, unplugging the battery when ever i plug/unplug. Unplug airbags, play around sitting on seat and measuring various points, get bored, clear out all the error codes with MES, plug it all back in, clear errors again. Whats the risks of the airbags going off?

Thanks in advance!

Alex

 

[mikeday1991]

Hey Alex,

Good luck with all this!
In terms of the signals the OCS sends, i'm not your man, as much as I'd like to be I havent had the time to study it all!

In terms of the plugging/unplugging mentioned, I unplugged and plugged my airbags back in whilst fiddling around and shorting out all sorts of wires & soldering etc, but when I plugged it back in, it was all ok.
My (Un)educated guess is: With everything disconnected from the battery, do whatever you like, but either put it all back together as it was before you started or better yet, as it came out of the factory, and you shouldn't have a problem when reconnecting the battery.
My car instantly recognised the OCS sensor, and I didnt have to reset or recalibrate anything on MES!

 

[ale199020]

The idea was to unplug all the explosive bits and then reconnect the battery and then ' play ' from there. After that disconnect bat and put it all back to normal. I just want to find out possibility of the system somehow setting off the bags belatedly

 

[ale199020]

Well I began down the path to airbag fault freeness today and I think I may have arrived! And all I did when I really think about it is give the damn thing a bit of a clean!

After looking on MES and having it show that OCS sending a unknown signal aswell as telling the ECU there is a passenger present when the seat is empty (my invisable friend must of gained some weight!) I took the seat out and apart and had a goosey at this OCS. When I took it off the foam I found it had been stuck on by two strips of very sticky double sided sticky tape, one at the top and one at the bottom, which were very lumpy. So I cleaned that side of the OCS up (during this time the fabric that goes on top of the OCS was still attached to it). Went back to the car, plugged it in and boom! No warning! So I sat on it....Warning.
Back inside I take the OCS. From looking at it I can't possible see how these things can really go wrong. They are all sealed in plastic, even the board, so i'm convinced its something causing it issues rather that it itself (if that makes sense). Having cleaned the connectors multiple times I decided to give them one last go so I remove the pins from the plastic and give them a quick go over with sandpaper (both male and female parts) and then add a small bit of solder to where the wire is crimped to the pin. The wires in mine looked like brand new wires so I'm now convinced the connection is good. Another blast with the contact cleaner to be sure and back to the car. Still a warning although this time it only goes off once I stand back up. Progress!
Off I pop back to the kitchen table and remove the covering fabric. What is left is what appears to be salt crystals and it has left a very bumpy and uneven surface on the OCS, not noticeable with the fabric on but very apparent with it off. After sometime scrapping very carefully with a knief and then a good rub down with yet more contact cleaner (they should warn you about getting high off this stuff) I take the OCS back to its cushion in the car and test again. No Warning. Stand up. No warning. Sit down. No Warning. Check MES, no warnings, person present!
Not wanting to celebrate too soon I got a helping hand to come and press on it with their hands rather than sitting on it. Still no warning!

My theory is that the salt (or what ever it was) crystals were somehow pressing down the pads and wires in the sensor distoring the signal somehow which then cause it to send a bogus signal down the line. Once cleaned up it was flat and happy again.

I've now glued the sensor back into place and waiting on the glue to dry for tomorrow when it all goes back into the seat properly to see if it has actually worked. I'll let you all know tomorrow!

 

[ale199020]

Just a quick update. Airbag warning freedom was not to be. After the glue dried I plugged it all back in and tada! Beep! Beep! Beep! After buying an emulator to get it through its MOT I did some more playing around and narrowed the issue down to about 4 of the pressure sensors in the rear 2 lines of the pad (as if it was in the seat). Just wear and tear as thats where a passengers rear end is most likely to be parked! I think when I was doing initial testing I must of been sat on the front part of the pad only hence the illusion I had fixed it. I might have a go at getting to the innards of the OCS at somepoint but fairly sure when I try to pry the two bits of plastic apart i'm going to tear up all the wiring inside so not holding out much hope.

Just thought i'd post that up so that people don't read this thinking its a fix and waste their time too!