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DIY: 1998 BMW 528i, Replacing Driver Seat Belt Buckle (Pretensioner)

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#1 · (Edited)
DIY: 1998 BMW 528i, Replacing Driver Seat Belt Buckle (Pretensioner)

I have Air Bag Light on the dash for almost 2 years now. Scanned with Carsoft Version 6.50.

Related thread here "Any Carsoft expert here? Codes 16, 24":

http://www.bimmerfest.com/forums/showthread.php?t=449818



It turned out to be Driver's Buckle (aka "Pretensioner").
PN 72118240045: $150 at local BMW Dealer. Don't even try to buy this online, because of the explosive charge inside the assembly, most online vendors won't ship it. So buy it from BMW dealer only!
This part varies from year to year, so ask your BMW dealer for help, or you can use realoem.com (enter your VIN).

When you have the Air Bag Light, it could be many things. You need to scan the codes.
Most people here use Carsoft Version 6.50 because it is cheap (since it is not the real version).
1. Pass seat sensor (search forum)
2. Crash Sensor(s), Front or Side: initially I thought this was the case and replaced it, see pic.
3. Seat Belt Buckle. BMW designs an explosive charge into the assembly, in a crash, the explosive charge is fired and this will pull the steel cable downward, tightening the belt, limiting the driver torso from going forward too far. I am not too sure this feature makes any difference because my Volvo and Honda buckles do not have this feature (explosive charge).



For those curious where the side crash sensors are located, they are under the front seat. Instruction for Front Seat removal is below.
http://www.bimmerfest.com/forums/showthread.php?t=459397
Again, this part (side impact sensors) rarely goes wrong, so I included here only for reference:





Options:

1. Do nothing, just placed a black electrical tape over. This is what I did for 1 year because I know it is the driver's buckle and nothing else, so worst-case scenario: during a crash, the seat belt will not be tightened further, similar to other cars I have so no big deal.

2. Fix it! Finally I have some time (and money) and decided to fix this.
Also special thanks to "bimmerteck" for his advices before doing this job!



Parts:

PN 72118240045: $150 at local BMW Dealer.

Tools:
- Torx Bit T30 (used with 1/4 ratchet)
- Torx Socket T50.
- 10-mm wrench for battery
- Screw driver, Pliers etc.
- Piece of 2x4 wood 8 inches long
- Zip Ties

Warnings:

- At appropriate time, you must disconnect the battery ground cable. Read on.

Procedures:

1. Move Seat all the way back.

2. Remove "Cosmetic Cover" using T30 bit. On the INNER side, it is tricky with tight clearance, so use a 1/4 ratchet. Then wiggle the plastic cover forward to remove. Now you have exposed the T50 bolts holding the driver seat frame. There are a total of four (4) T50 bolts: two (2) in Front and two (2) in Rear.



3. Remove two (2) T50 Front bolts. Then move the seat all the way Forward.

4. The two (2) T50 Rear bolts are under a plastic cover. Gently pry the plastic cover up and remove it (it just snaps in).



5. Now there are two (2) ways to do this, some people remove the seat from the car completely, but I find this is more work than necessary. I did this with the seat in the car using a piece of 2x4 wood that is 8 inches tall.
Since you will move the seat further Back, you will need to undo the "seatbelt height adjustment cable" thingy. Under the seat, there is a cable that connects to the seatbelt height adjustment. The "Fixing Pin" rotates and locks into the "Fixing Clip". Note how it is setup for re-assembly. Simply rotate the "Fixing Pin" to unlock it. Then pull the "Fixing Pin" out. The "Fixing Clip" will come off.
Confused? Look at the opposite seat for reference.



6. Now Pull the seat as far back as possible (watch the wiring coming from the floor, don't yank it!).
Place the 2x4 wood under the rail to lift the seat up. This allows the T50 socket to go in to remove the Pretensioner.



7. Now, STOP! Go to the trunk and disconnect the Battery Ground Cable (10-mm wrench).

8. In order to remove the old Pretensioner, you need to:
- Undo the Velcro
- Cut the Zip Tie
- Disconnect the 2 connectors (1 for explosive charge and 1 for buckle). They are very easy to disconnect.



9. Now look at the old and new Pretensioner:
- Old Pretensioner has "wire chafing", this may be why I have the above SRS codes.
- New Pretensioner has Protective Sheathing.
- Transfer the Old Plastic Clip to New Pretensioner.
- Connect the 2 connectors
- Add zip tie.

10. Now, install the New Pretensioner: there are 2 notches (Blue arrows) that must match the tabs on the seat.





11. Re-connect:
- "Seatbelt height adjustment cable" thingy.
- Battery
- Four (4) T50 bolts
- Cosmetic covers
- Velcro around the base of the buckle

12. Get Carsoft Version 6.50 to turn off Air Bag Light.
A few tricks on Carsoft 6.50:
http://www.bimmerfest.com/forums/showthread.php?t=345629
http://www.bimmerfest.com/forums/showthread.php?t=449937

The bottom line for me:
- Laptop Compaq Evo N600C from 2003 with the 9-pin RS232 port
- XP Operating System
- Install software as instructed: copy from disc to C:\. See attached pdf.
- Then copy the 10 "crack" files as instructed.
- You must launch Carsoft from C:\cm75f directory. If you launch the software from "Start\All Programs\Carsoft", the software will crash LOL! So, for this part of launching software, do not follow the pdf file.
- Go to C:\cm75f directory, find the Carsoft.exe file and launch the software from there. Listen to me, it took me a long time to figure this out!!!
- Battery must be fully charged!
- Key in Ignition Position II
- Erase Air Bag codes.
- Go to dash, the Air Bag should be off.





That is it, boys and girls!!!
 

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#3 ·
Doru,

In Step #10, I showed the picture of "Chafed Wire" near the Buckle.
That was the problem. I cannot understand why a Chafed Wire can do this.
The insulation is stripped but the wire is still OK.

In theory I could have fixed it by using new wire etc. etc.
But since:
a. This part is 14 years old and has seen 125K miles with thousands of clicks at the mechanical part (the Buckle).
b. My life rides on it during a frontal crash.
c. The explosive might have lost its charge (I may be wrong). This "invention" by BMW....I kind of doubt if it makes any big difference in a crash.
Many cars do not have this explosive thingy and still pass federal crash tests.

My concern was #a above: what if the buckle does not hold during a crash ----> the driver will R.I.P.
With the new Buckle, it has a distinct new sound "click" that sounds very good LOL. I am happy with the new "click".
 
#5 ·
Thanks doru,

I just uploaded a document on Pretensioner (see attached pdf) that shows pic of deployed pretensioner.

I'd be curious to know:

1. Who first invented the pretensioner idea. Is it 1980s or before that?

2. Does it really help in a crash testing experiment?
 

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#6 · (Edited)
DIY Passenger Seat Emulator

I forgot to post the DIY Passenger Seat Emulator.

Bought the BMW Passenger Airbag Seat Sensor Mat Occupancy Bypass Emulator from ebay seller radzos from Vilnius, Lithuania; $10 + $5 shipping = $15 total.

It is a very simple fix:

1. Open Right Rear Door and look behind the Front Passenger Seat.
- Cable that goes to SRS Computer is Blue.
- The other connector goes to the seat sensor (Red).

2. Unplug the factory connector (squeeze the side tabs and pull) and install this "Emulator".
Then zip tie the factory cable so it does not hang down.

Done in 5 minutes.
Then use appropriate software to erase the SRS dash light.



 

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#7 · (Edited)
UPDATE to this whole thing.

Initially, the Carsoft SRS Code was:
24 Linker Sattellit (Sidebag Sensor) / Druck-Fuhler, Beifahrer Airbag
16 Gurt Schalter, Fahrer Airbag


1. I researched and someone told me it was driver's Buckle (aka = Pretensioner).
Installed brand-new Buckle.
The SRS codes came back.
This time I gambled and bypass it using the "Emulator" as mentioned above.

2. The new "Emulator" works great!
SRS codes never came back.

So if you ever see the above SRS codes in Carsoft, the culprit is the pass seat sensor!

PS: Now I have a brand-new Buckle LOL.
Considering that my life rides on the Buckle (in the event of a frontal collision), it is not a bad thing to have a brand-new Buckle after 14 years of service!

------------------

This is my understanding: this whole thing about pass seat occupancy sensor is to prevent injury to a child < 40 lbs in a car seat placed in the FRONT seat.

Factory Setup:
- Adult Passenger FRONT Seat: sensor tells SRS computer that there is an adult there, in a collision with more than 7G deceleration: pass airbag deploys.
- No adult: if sensor does not sense anything more than 40 lbs: pass airbag will NOT deploy to prevent potential injury to a child (should there be a child less than 40 lbs there).

My mod using "Emulator":
- The Emulator simulates condition that there is an adult there. So in a collision, the airbag WILL deploy regardless if there is any pass in the front seat.
- So if you install this Emulator, do not place any child seat on the front.
Actually, if one searches the internet, even the government strongly recommends a child less than 40 lbs to be placed in the REAR seat, it is much safer there.
It does not matter what car you drive, a child less than 40 lbs do NOT belong in the FRONT seat anyway!

I am a safety-conscious person and I am confident using this mod.
 
#8 ·
Wow. I didn't know about this DIY until now ... so ... as I am wont to do ... I just added the following to the existing bestlinks on the topic so that others will find this more easily in the future:

- What is the cheapest usable BMW E39 airbag srs reset/scan tool on the net (1) & a DIY for replacing the driver seat belt buckle pretensioner and the passenger seat emulator (1) & what can cause a BMW E39 SRS airbag light (1) (2) (3) (4) (5) (6) & what scan tools reset the fault (1) (2) (3) (4) (5) & what happens when we disconnect the airbag before the battery or we connect the battery before disconnecting the airbag in seat and window regulator repairs (1) (2) (3) (4) (5) (6) (7) (8) & where to obtain an airbag occupancy sensor bypass unit (1) (2).

Note: Here is the cheapest SRS reset tool that I could find to date:
 
#9 · (Edited)
For cross reference, this was posted today in the E38 forums:
Error 16 => Driver***8217;s seat belt buckle switch
I tried to do a search about this code but results were very poor. For this reason I am writing a few tips, maybe there is somebody to find this helpful. For those that are out there and experiencing the BMW code 16 for the airbag: simple fix, that worked in my case, some contact cleaner and 2 minutes of my time. I took the seat belt buckle, sprayed contact cleaner until it was full, clicked the seat belt in and out as much as I could for about 2 minutes. I used about half spray can, reset the code with INPA and no Airbag light anymore. Apparently there is a circuit board inside that gets dirty or looses contact with time and clean it solved the problem. In worst case the seat buckle has to be changed, about $125. There is a TSB about this issue which I found available here: http://www.netropy.com/stuff/SI-720496.PDF
.
And, this was posted today in the E46 forums:
Hey, I'm just wondering what a good and a "blown" seat belt pretensioner look like vs one another.

I know what it is and what it does. so it looks like the one on the passenger side is bad to me.

but when the vehicle had it's collision no one was in the passenger seat and the belt was not buckled. Although the steering wheel and dash airbags both deployed.

passenger side shows more of the cable protruding from the cylinder then the driver side.

The SRS light was on for about 5 years before the collision, never could figure that one out.

If the pictures aren't good enough let me know, and i'll go try to take some better shots.

A little advice would be great.
Thank you~!
 

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#10 · (Edited)
driver' s side seat (mat) sensor wires are where in a late modle E39 (2002)

Bluebee, or anyone, you have a 2002 model. Have you seen this blue/ white mat sensor connector and wires? I was under the back(rear) of my 2002 sport seat and only saw a larger conduit, centrally located with many wires and a connector farther fwd with a brown/ red wires. Broke my neck looking with lights and m:mad:irrors. Looked under the front as well. ****PS- after some more research, I found the wiring harness to be different after 02/2000. So, looks like a bypass is not possible at first glance. After reading the nice write up by cn90, above, I'm double checking the small wire on the seat belt upper pre-tensioner for any wear.
 
#11 ·
Just had a minor crash. The car that I hit was fine. Mine too, a few scratches, but nothing more than the stone chips already. I guess both bumpers did their job 'cus the crash was somewhere around the 30's. But my light went on and then I noticed that the buckle was way further down. So I don't have any collisions involving cars with no pretensioners but I know it's there for a reason. It might be very insignificant in some cases but it might make all the difference one day- hoping never to speak from that kind of experience. It's a freaking expensive thing but, i think it's worth it. And technically it's not a very complicated thing, so I'm thinking even buying one out off ebay for half the price, but will see.
Thanks for the DIY it will be very helpful.
 
#15 ·
Side Airbag LIght on.

I have a 2002 BMW 530, (E39). My airbag light is on, and it is throwing a code that says it is the passenger side airbag sensor. Note, it isn't the "seat occupancy sensor", but it is the side airbag sensor. I have searched this forum and didn't find a link on how to replace it, but I did find that it was under the ductwork under the passenger seat. I have ordered a used one from Ebay. I have taken all the hardware off of the passenger seat, and it is ready to be lifted out. My question is......How do I remove the carpet without damaging it? Do I take the door trim molding off at the threshold of the door and peel it back? Anyone done this before?

Thanks.
 
#17 · (Edited)
Just for the record, I was looking up SRS airbag information for someone when I noticed the absolutely gorgeously detailed pictures of SRS components in this BMW SRS Marketing PDF ...


See also:
- How do BMW Supplemental Restraint Systems (srs, airbag, bst, crush zones, etc.) really work (1) & what is the cheapest usable BMW airbag srs reset/scan tool on the net (1) & what other scan tools reset the fault (1) (2) (3) (4) (5) & what can cause a BMW SRS airbag light (1) (2) (3) (4) (5) (6) & a cn90 DIY for replacing the driver seat belt buckle pretensioner and the passenger seat emulator (1) (2) & where to obtain an airbag occupancy sensor bypass unit (0) (1) (2) & what happens when we disconnect the airbag before the battery or we connect the battery before disconnecting the airbag in seat and window regulator repairs (1) (2) (3) (4) (5) (6) (7) (8)
 

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#19 ·
CN90 and Bluebee, though this post is 2 years ago its the only thing i can find close to my issue. I did the dresded take seat out without disconnecting battery. I did this to add a seat heaer for my wife. I put it back together and got SRS light. I went to a local indie for yearly inspection and to turn light off. He tried 3 different times and i wouldn't trun off. It said pretensioner was bad. Any idea why or if I overlooked a connection? The only wiring I disconnected was under the seat in front where all controls come from. I didn't knowingly disconnect anything new the buckle or tensioner. Am i missing something obvious? If i need a new tensioner that's ok but it didn't seem right. CN90 where did you order yours? Thanks for any help guys I tried to follow thw forum rules by searching first but coldn't find anything about wire connections associated with the tensioner or any other wiring.
 
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