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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 03-03-2010, 12:57 PM   #1
kraimer
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DIY - BST - Battery Safety Terminal

First a little history of what a BST is; essentially BST is an "explosive" connection which gets triggered during collision which disconnects the cable that runs to the starter. Explosion obviously cannot be heard nor felt, but you can see from below pictures that explosion is definitely present. I tried finding an answer to "how much force actually triggers the explosion", but couldn't find it anywhere. I was rear ended on the highway back in October (by a 535...), my airbags were not triggered, the seat belt tensioned, the car shut off and hazards went on. When I tried starting the car, it wouldn't start so I had to get it towed off the highway. A little search on e46fanatics, screw driver and some duct tape got my car started again... I basically opened up the plastic housing that covers the connection, inserted male and female ends into each other taped it up and drove around like that before my car was fixed at the shop. The body shop never replaced the BST, even though we had discussed it when I dropped the car off; however after I picked up my car and realized they never replaced it, we agreed that they will provide the cable and I will put it in myself – the part itself is over $500…



part no. 61128387512 and realoem list price: $500.98


Ok, enough with the rant and onto the diy…




the cable as it comes in the kit.

the very first thing you need to do is line up the replacement cable right along the existing cable and mark where the existing cable should be cut - make sure you give enough room for the screw-in connection. It's better to make it just a little longer than it not reach or be very tight at the battery...



just to reduce the amount of pictures, I collaged them...

1) cut and remove about 5/8" to 3/4" of insulation from existing cable
2) insert the cable into provided threaded rod
3) slide "collar" over the threaded rod
4) install provided nut and tighten until "collar" and the rod end line up
5) screw in replacement cable into the new connection you just made in the existing cable







a thick heat shrink tubing is provided with the kit that you "melt" over the connection. this tubing requires a loooot of heat, a regular lighter will take you forever, butane lighter or a heat gun will work best. I wasn't comfortable with just the heat shrink tubing so I wrapped it with a few layers of electrical tape



replaced cable




as well as I was able to take a picture of the female side of the connection - you can see the grey deposit from the "explosion"


Hope this helps someone...
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Old 03-03-2010, 01:18 PM   #2
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didnt know our cars had this safety option very interesting
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Old 03-04-2010, 06:26 AM   #3
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I also had no idea until the accident...
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Old 04-02-2010, 03:50 AM   #4
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thanks buddy im doing one tmorrow, but got a full cables from a breakers, non deployed. And will splice it in the pics are gr8

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Old 07-09-2010, 06:08 PM   #5
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Hi,

I did this diy tonight and I found it very difficult to fit all the copper wires inside the threaded rod, how did you manage to fit them all in and keep them in whilst using the required force to screw the nut?

My copper wires are all frayed and most of them are actually outside of the threaded rod.

I've left some excess length so I can give it another go with your advice!

Thanks
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Old 07-10-2010, 04:38 PM   #6
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This is pretty cool. I wasn't aware we had this. It comes stock on all e46's?
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Old 07-11-2010, 11:24 AM   #7
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You can look the part no. up on www.realoem.com and it lists the application.

It is stock on all e46's

MSRP on that bad boy is now $528.56 and Tischer sells it for $422.85
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Old 05-03-2012, 10:01 PM   #8
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Can be had for much cheaper now if you use www.furiousmethod.com
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Old 08-16-2012, 09:30 PM   #9
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It took 2 people and an impact wrench for me to do this. The amount of torque required to get the sleeve over the threaded cap is ridiculous not to mention keeping the cable in as you do it. All in a small space. We found the easiest way to do this step was to hold the cable end in one hand and a crescent wrench on the sleeve in the other. Then have the other person use the impact on the 22mm nut to force it on there. Works like a charm. By the way my cable frayed out also but works fine. Hope this helps.
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Old 09-25-2014, 08:03 PM   #10
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Exploded BST cable

Took my 545i into the shop last week and they told me that the bst cable exploded on its own without accident or without incident. Anybody run into this issue?
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Old 10-02-2014, 02:10 PM   #11
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Why did you take it in? Wasn't starting? How reputable is the shop? Not saying they did it, but also not saying they didn't...
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Old 11-27-2014, 10:33 AM   #12
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Is there a real need to replace this part? I'm doing a minor collision repair on my sierra metallic red 323i 5spd from a 99 auto tran 323i with tranny/paint issues(Scooped it for parts for 1k)(auto's use mechanical fan instead of eletric and have a different piece on the radiator the expansion tank clips to ) but has been resolved be swapping the plastic piece from damaged 5spd radiator as well as the different plug(auto tran plug broke removing it had to drill/crumble it out to put manual radiator plug in be careful...)

As for this bst I kind of don't want it, In the acident i was just involved in I Could have easily moved my car out of the road/out of traffic, but due to this device i was unable to. I think its really to prevent people from fleeing an acident as much as "Safety", if i was hit on the freeway and car ended in spot it was in danger of being struck again I'd want to move the hell out of there if possible before exiting vehicle...

So my plan is to bypass it instead of swapping it in and selling this very overpriced part, is there any concern of doing this?
what sensor or signal wire tells the bst to blow? Is the physical disconnection of this wire what shuts the car off(lights and auxillary power remain on for hazards/unlocking door/cabin lights) or is than handled by srs ecu and this just disconnects starter from turning it back on? I assume a signal comes from the srs ecu to blow it, but if the recieving end of this signal is no longer attached there will it throw an srs light for example? I Have a peake to reset or see if it does but just wondering what i'm getting into (msg if you ever need to use the peake in southern ma!)

Also if like op i was rear ended in daytime and damage was minor I'd be rather angry to call a tow home esp if close by and very driveable...

and if this is doable why do more e46 owners not do it to pocket 300$ for a cable... other than because it's pulling pieces from your car

Last edited by hatetolovee46; 11-27-2014 at 11:19 AM.
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Old 11-27-2014, 11:31 AM   #13
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Quote:
Originally Posted by hatetolovee46 View Post
I think its really to prevent people from fleeing an acident as much as "Safety", if i was hit on the freeway and car ended in spot it was in danger of being struck again I'd want to move the hell out of there if possible before exiting vehicle...

So my plan is to bypass it instead of swapping it in and selling this very overpriced part, is there any concern of doing this?
I think it's rather far fetched to imagine that the BST was installed to prevent 'skips'!
That aside, I'd have no hesitation to remove the unit from my car if faced with the replacement cost. Naturally you'll never get any official recommendation toward this end due to liability issues. But in my opinion this is a rather low yield in the cost vs. benefit calculation. How many fire conditions have we ever seen in a crash situation credited to a battery cable? Not many, but probably a more common event if you were a firefighter.

Can't protect against everything, and I'D take my chances.
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Old 11-27-2014, 01:41 PM   #14
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I completely agree stinger, but i just think if auxiallary power remains to auto turn on hazards/unlock doors and turn on cabin lights what power is this actually disconnecting? i believe it ONLY disconnects the starter... which doesn't seem like a fire risk unless you are trying to start your damaged car leaking flammable fluid(If car is damaged to that extent it shouldn't turn on or you shouldn't be trying to turn it on anyway...)

or as an idiot proof mechanism to stop people from trying to start car if pully's are jammed/bent in front or something?

I'm not really sure, all i know is what little benifit it could provide I (Personally) believe is outweighed by not being able to move your car out of a dangerous spot after a minor accident
This along with it having a used value of around 300$ is enough to not replace mine, or if i had thought of it before the accident remove entirely.

BYPASS IS DONE:
TO BYPASS A BLOWN BST: there is a terminal almost exactly like your battery terminal in the black plastic bst housing. it sits in a metal cup fully touching the terminal on top and all sides for good connection(ever try to start yoru car without + terminal on tight only to realize power dies instead of car starting? ) at the bottom of this cup there is a small charge probaly smaller then the charge in a .22 round that explodes and pushes the terminal out of the cup disconnecting the line. you can litterally push the terminal back into the cup with blown charge TIGHT and the car will start (my srs light is still on need to change airbag not sure if there is an srs code along with this or not...)
TO BYPASS GOOD BST: you will need to cut the bst out and use HIGH quality cable connectors and attachments. these are common and cheap items in the car audio industry(power cable splices and terminal crimps)

^ again if there is an srs code to go alone with this i will edit and repost, niether of these options will work other than getting your car to start without the airbag light coming on if there is, the bst does have a wire harness going into it...

Last edited by hatetolovee46; 11-27-2014 at 01:42 PM.
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Old 11-27-2014, 02:39 PM   #15
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Quote:
Originally Posted by hatetolovee46 View Post
i believe it ONLY disconnects the starter... which doesn't seem like a fire risk unless you are trying to start your damaged car leaking flammable fluid(If car is damaged to that extent it shouldn't turn on or you shouldn't be trying to turn it on anyway...)

TO BYPASS GOOD BST: you will need to cut the bst out and use HIGH quality cable connectors and attachments. these are common and cheap items in the car audio industry(power cable splices and terminal crimps)
Couple of comments.
Yes the battery cable that is disconnected feeds up to the starter and then on to the alternator. But this large cable that runs the length of the car is the most likely to start a fire in that the fuse is huge and the cable will not easily melt away in the event of a short, as a tiny wire might do.

And yes you could cut out the BST, but not only will you need a high quality cable connector, but the glitch is that most people will not easily have access to a crimping tool for very large cable connectors.
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Old 11-27-2014, 04:46 PM   #16
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^ this seems very true and thus likely the reason the bst is there, due to this i concede and would probably not bypass this, After installing positives and grounds for car audio in my car the bypass seems like it would be a cakewalk to me but yes i could see most not having that crimp tool. It does not however matter either way as a blown bst throws an 02(Chart) OE(firing circuit:battery disconnect) code with the bst bypassed(the car does start normally if you need to do this to test car). an experience srs techniction(not myself or you...) could find the state of the wires to the wireharess of one operating correctly(without interfereing...) and compare with one with this code and likely bypass the harness, however this is far outside what i would be comfortable with or any diy'er should be comfortable with as you'll very likely blow the working one or worse, bottom line is we should prob just pay the 300-400$/pop... and after examing the bst this is a HUGEEEE rip off it could be made for 5$... it just a little .22 cap charge in the bottom of the cup...

edit* they can be grabbed used but not blown on ebay for 100-150 it looks like

Last edited by hatetolovee46; 11-27-2014 at 04:55 PM.
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Old 10-02-2015, 10:46 AM   #17
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I believe the BST on my Wife's car is failing , although it is not blown. The car intermittently clicks, I have went through all diagnostics and nothing is popping up in INPA, voltage is fine, no EWS errors. Can you doodle up your bypass strategy please?
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