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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 06-14-2010, 02:17 PM   #1
Scott87
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Exclamation Airbag Occupancy Sensor Bypass Unit DIY (pics)

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!!

Last edited by Scott87; 06-14-2010 at 02:19 PM. Reason: Image Link
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Old 06-14-2010, 03:50 PM   #2
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Great DIY. I did this a couple of weeks ago and it works like a charm and its super easy.
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Old 06-15-2010, 12:28 PM   #3
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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!!!!!

Last edited by profor; 06-15-2010 at 12:36 PM.
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Old 06-15-2010, 12:35 PM   #4
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I could have done with knowing the resistors rating before I bought it off ebay... oh well lol. I measured it myself out of curiosity when i got it.
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Old 06-15-2010, 04:04 PM   #5
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Todays mod - used 4k7 resistor





Last edited by profor; 06-15-2010 at 04:13 PM.
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Old 06-15-2010, 05:23 PM   #6
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Cool. So you took the unit out and mounted it internally. Saves having an extra wire kicking about under there. Looks tidy.
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Old 06-16-2010, 06:41 AM   #7
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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

Last edited by profor; 06-16-2010 at 06:46 AM.
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Old 07-10-2010, 09:49 PM   #8
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profor, you do some kick ass work man, are you a electrician ?
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Old 07-10-2010, 10:40 PM   #9
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subscribe. i will do this next week.
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Old 07-11-2010, 04:56 AM   #10
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Yes, i am but not in car service, i am just interested in such stuff and i am not afraid to do these things on cars

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profor, you do some kick ass work man, are you a electrician ?
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Old 08-04-2010, 06:03 PM   #11
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bookmarked if my seat sensor fails again, thanks!
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Old 08-04-2010, 09:39 PM   #12
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do you guys know how to do this for someone with racing seats in their car? ?

Thanks.
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Old 08-05-2010, 12:02 PM   #13
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Quote:
Originally Posted by dakkon View Post
do you guys know how to do this for someone with racing seats in their car? ?

Thanks.
Would have to pull the electronics out of your stock seat and wire it in. zip it to the underside of your seat. I need to do this as well as mine went out like 6 months ago.
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Old 08-16-2010, 08:35 PM   #14
haurelio
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would this work for the seatbealt tensioner faulty code?
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Old 08-17-2010, 07:03 PM   #15
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No, there You just need to connect, instead of seatbelt tensioner, 4ohm resistor.
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Old 10-13-2010, 03:02 PM   #16
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Thumbs Up Great DIY instructions

I just finished installing the bypass unit and it took about 15 minutes. It helped to unbolt the seat to better see underneath.
thanks!
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Old 10-13-2010, 03:20 PM   #17
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Where is the link on ebay?
Will the light turn off by itself?
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Last edited by RockLee; 10-13-2010 at 03:42 PM.
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Old 10-15-2010, 09:46 AM   #18
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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.
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Old 12-08-2010, 04:50 PM   #19
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Quote:
Originally Posted by profor View Post
Todays mod - used 4k7 resistor




Hi profor i tried this just now with a "n14002" diode and a 3k3 resistor and the light is still on? can you make any suggestions what i have done wrong?
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Old 12-08-2010, 05:54 PM   #20
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Quote:
Originally Posted by profor View Post
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
ehmm what is that program? how does it work?
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