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DIY: Airbag Occupancy Sensor Bypass Unit

263K views 92 replies 44 participants last post by  bhunter10 
#1 · (Edited)
Well, every time I had a passenger in my car I got the really annoying airbag light on my dash. This is due to the sensors in the passenger seat failing or having failed. The seat has a mat inside it that can detect the presence of a person. Now this has broken the ECU detects that and puts the airbag light on. The bypass units can be bought on ebay very cheaply, mine was £5 delivered. They are basically just a small resistor to imitate the resistance created when a passenger sits in the seat. They are used to control the deployment of the passenger airbags. A crash with no passenger means no passenger airbags deployed saving on repair costs. Now this unit is fitted the airbags will always deploy as it always thinks there is a passenger (better than the other way round). The only downside is now you can't put a baby seat up front due to the airbag deployment. This, however, wasn't an issue for me and is way better than the £480 BMW wanted to fix it.

Any way, on with the DIY!

You will need:

Airbag occupancy sensor bypass unit
Maybe some tape/zip ties
Snips

Okay first up you need to roll the seat forward as far as possible then tilt it forward as much as you can. You don't need to go mad and push it forward there should be enough room if you lay down on the back seats. In this picture my fingers are on the connector unit that you will be working on:


If you look under the seat its right on the back side closest to you, ignore all the cables in the middle underneath. This is the unit you need to find:


At the top of the image above are a blue and white wire. These wires come out of the box (left side as you look at the image) and in to a connector block. The right side of the connector block needs to be unclipped and pull as much slack as you can out. This is the connector hanging down here, excuse the really bad photo:


Here is the connector cut off, leave yourself a couple of inch of wire on it:


Here is the bypass unit I will be connecting:


Mine came with some crimping blocks that needed to simply have each wire inserted and crimped shut. You may need to strip and twist them together then insulate with tape. Either way is fine and should look like this:


Now simply plug the connector back in to the unit and zip tie or tape the wires out of the way. Enjoy no more airbag lights!!
 
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#3 · (Edited)
if somebody is little bit more skilled, he can do it himself and not buying things from eBay.

I did some research by measuring the ocupancy sensor which was okay, and figured out which components You need to bypass the sensor if it is broken.

So You need soldering iron, not shaking hands and one 3k3 to 30k resistor and diode 1N4007.

schematic diagram is in the picture



CAUTION:

this is modded bypass modul that was previously posted on some forums, but that "OLD" one caused the airbag light off but the seat was in control unit of airbags NOT OCCUPIED. therefere I did this mod which will make the seat "OCCUPIED" even if nobody is there!!!!!
 
#44 ·
Reverse Occupancy sensor




Hey buddy,

I want to turn the airbags off as i want to put my child in the front (he is a nightmare to keep entertained) Im thinking, if we can trick the occupancy sensor to say the is always a passenger, we can also trick it to say there isnt one.

Does anybody know the resistance of the sensor if no one sits in the seat?

Then i make a resistor up for that and off we drive.

Kind regards

Matt
 
#4 ·
#7 · (Edited)
Thank You,

yes is tiny, original blue/white cable is wound up inside, so it looks like nothing happened to it, also the sensor is connected.

Not occupied seat

Not okay - happens if the sensor is broken

Occupied - this state will have CU after installing the diode and resistor as i posted here
 
#18 ·
My light turned off but some people need to have it reset. This shouldn't cost more than £10 really but expect to pay a little more if they are out to rip you off. It's a 2 minute job to reset.
 
#23 ·
basically the same idea.. i jus did but did a couple things different.. instead of taking off the wires from the module i just splice them and tap them together.. ( you can either do it inside the box or outside)
 
#26 ·
Cool thanks for that info.....you say you did not bother opening the little black box. you just tapped the blue and white wire's together without a resistor and diode? or do i not understand you correctly?.
Also after doing this should the light go out by its self? or do i need to have it reset with a computer?
 
#27 · (Edited)
no thats' not correct.. i did use the resistor and diode.. this is pretty much what i did..http://s772.photobucket.com/albums/yy6/haurelio/?action=view&current=_IGP7469.jpg.. and then i just kind of use the shrink plastic and black electrical tape..now just keep in mind that this will work only if you have not unplugged/disconnect the internal blue and white wires.. and as far as the light. it should go away by itself ( no always the case).
 
#53 · (Edited)
The light will defo go out with the old circuit i.e. 2 100ohm resistors in series with the diode. However, I dont think this makes the seat 'OCCUPIED' and that is what I am trying to resolve.
Floorjacker - you say that you have tried them all but did you reset the codes man?
Hi, I'm a seller of these on eBay and I see you are actually a seller on eBay of these items as your username is the same as this previous name and is also from Preston. You have used 2 accounts and here are the links below with snapshots also. It's obviously you due to the randomness of your username and coming from the same location

http://contact.ebay.co.uk/ws/eBayISAPI.dll?ReturnUserIdHistory&requested=airbagmodules



http://contact.ebay.co.uk/ws/eBayISAPI.dll?ReturnUserIdHistory&requested=a3_thr




This is a picture of one of your items that someone recently bought from you so can I ask why you don't clearly state that airbag WON'T deploy seeing as it's not even got any resistance in it?




here is a link to a more informative post about this on a 5 Series forum as this is where I got your item from

http://forum.bmw5.co.uk/topic/64274-airbag-occupancy-sensor-bypass/page__view__findpost__p__674393


Strangely you did ask people if they were Are you concerned that your airbags may not deploy in the event of an accident? as shown in blue text in this item below. Whereas in your current listings you've now removed that question for obvious reasons

http://www.ebay.co.uk/itm/190637462530

I know you've got a disclaimer but surely you know it WILL NEVER deploy (you've got a typo for deploy by the way). Therefore don't you think that your buyers should be made aware of this seeing as most will have passengers?

What are the cons to bypassing the occupancy sensor?

Whilst the bypass unit will reactivate the airbag system (if it's even disabled in the first place), there can be no guarantees that the passenger airbag will depoly in an accident. We have spoken to different BMW Technicians and there is different opinion regarding this. The buyer would be accepting this by clicking on 'buy now' button. It must always be remembered though that this is only a short term 'workaround' and not a long term fix.
I hope making you aware that quite a few people are now know what you are selling will possibly make you change your ways :thumbup:

Cheers

Mac
 
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