Mini Cooper Airbag Wiring DIY fix advice

langdang

Hi all,

Has anyone else had the following problem, and any opinions on what I intend to do to fix it?

DISCLAIMER:
This thread involves messing with wiring for lifesaving safety equipment. For future readers of this thread, don't attempt anything here unless you know what you're doing and can filter good advice from bad advice! From my own point of view, I won't hold anyone but myself liable if I make a liathroidi of this.


PROBLEM:
Early BMW Mini models had particular problems with wiring under the seats for safety stuff (seat belt pretensioner usually, maybe occupancy sensor). This is fairly common on many coupe/hatches - with constant moving of of one seat or another, the wiring will occasionally break contact or see a high resistance for a split second and flag a fault. Even if the "fault" condition disappears straightaway, you're left with a fault light on the dash, and an uncertainty over what will work or not if it comes to it or if there are other more serious faults.

Three opinions on what causes the problem in Mini's
1) Wiring too short, puts too much strain on connectors at extreme ends of seat travel.
2) Connectors just generally crap, especially in some production runs
3) Wiring too long, resistance too near fault-trigger level.

In my case the light has been turned off several times, it is the seat belt pretensioner circuit everytime...
Previous owner has already been at this car with a bad soldering job and cheap insulating tape, so I reckon the following will hardly make things worse:

DIY SOLUTION:
Remove negative battery terminal and have a cup of tea.
Rmove connectors from where they clip onto underside of seat, see how much cable I have to work with.
Move seat back and forward to see if there will be any problems if they are left roam free rather than clipping to the front of the seat. I think this routing is putting strain on the connectors and transmitting any bumps to the seat straight down to the connection.

Cut connectors between car wiring and seat wiring, crimp cables together directly. (Don't like soldering cables that have to bend)
Heatshrink over the crimp, and existing solder job (if I can't also remove that).
Cable tie cables in sensible places.

Thinking of putting something in there to protect the wiring under the seat
-flexy tube around wires OR (complete over engineering but) if I had a small articulated cable chain, like you see guiding wiring in robots or industrial machinery....

Whole lot of text there, but has anyone done something like this? Anything I'm missing? Any tips?

I've created a separate specific thread rather hijacking or resurrecting other airbag threads.

Myrddin

The only disadvantage to doing it this way, is that if the seat ever has to be removed, your going to have to cut through your wiring. The connectors in the car are very poor, and as a job in BMW, you are issued with four new connectors and two lenghts of wiring. The connectors must be cut as you have outlined above, and the new section of wiring is added, which has the preattatched replacement connectors.

This way the wiring can be disconnected for seat removal in the future. There's nothing technically wrong with your approach, and it should be effective. Just a hinderance if your seat has to come out in the future.

bazz26

Not a good idea to go down the DIY route with this imo.

DIY work especially involving crimping cables together, etc on safety equipement like an air bag could mean that it doesn't work correctly anymore and posses a risk to the front passenger in the event of an accident.

Also messing with safety equipement is a big No No with insurance companies. If God forbid, there was an accident and the passenger air bag didn't deploy properly then any any post accident investigation would focus on this.

Gary ITR

Motors Forum Charter wrote: »

* This is a public forum used by people with no idea what they are talking about. Don't assume the advice given is correct. Maintenance tips offered by forum members, whilst helpful, may not necessarily be correct solution, so if in doubt then contact your nearest dealer or qualified mechanic. If you do something as a result of what you read here, you agree that boards are in no way liable for anything at all - you are responsible for your own actions.

Just to bring your attention to this part of the charter OP

langdang

Absolutely Onkle, pre-empted this myself in my own disclaimer.
I think if anyone who didn't know what they were doing starting randomly cutting wires to do with safety features it's just Darwin time if something goes wrong....

Hadn't thought of the insurance aspect.
The proper fix as described above is surely 200 - 300 in a dealers? If I was to be paranoid about insurance then dealer is my only option I presume.
They extended the warranty on this way out in the US but they have strict Lemon laws there. No attempt to rectify this in the UK or Ireland.

gofaster_s13

This thread should be locked up/deleted, an airbag going off at the wrong moment can seriously injure/kill and should not be tampered with unless following manufacturers guidelines to the letter(and even then only by people trained in handling airbags and associated systems), the method of repairing the airbag wiring that the OP posted has a couple of serious flaws and is in the whole very bad advice.

langdang

gofaster_s13 wrote: »

This thread should be locked up/deleted, an airbag going off at the wrong moment can seriously injure/kill and should not be tampered with unless following manufacturers guidelines to the letter(and even then only by people trained in handling airbags and associated systems), the method of repairing the airbag wiring that the OP posted has a couple of serious flaws and is in the whole very bad advice.

I'm not messing with the actual airbag, and I'm advising anyone else not to even attempt any of this unless they know what they're doing.

The BMW fix for this ( The TSB describing it is in the wild, as it is a VERY common problem) is almost exactly as I have described, except they have two (potentially flakey) connectors for convenience if the seat was ever to be removed.

If I do something wrong here then the system will flag the same fault as it always does. If someone who didn't know what they were doing did this then maybe something dramatic would happen.

gofaster_s13

There are a couple of key steps missing from your advice that would make working on airbags dangerous, you are not working on the actual airbag itself but the method you are advising could induce a static charge into the system which could(and occasionaly does) in turn cause the airbag to discharge, this problem is heightened by the fact that the Mini's are very prone to static build up(which was also the cause of an earlier recall on the Mini's)

Drummerboy08

I agree with Gofaster. Messing with an airbag is something I wouldnt fancy doing. In the even of an accident, it could fail to fire causing death or serious injury.

Or it could fire while your messing with it.

The best advice I can give is to bring it to a qualified mechanic.

Owen

I really wouldn't recommend this advice to anyone. I've more experience of this than you have OP, if you must extend the cables, crimping is not the way to do it either. Crimping gives you a connection which can be severed with force, as the only thing keeping the cables together is the metal compressed around the fragile copper. If the cable gets booted around too much, the copper strands shatter, and eventually, the cable can work its way free.

The correct way to do this, would be to continue to use BMW's connections, and on the cable between the floor and the first connector going up into the seat, cut it there (Battery disconnected, and everything grounded as much as possile, wrist straps, etc). Solder in an extension into this cable, and heatshrink all the wiring to make sure it is 110% insulated. This way you now have a longer cable, can disconnect the seat, and you're reducing the risk of the airbag deploying by not working on the seat, or it's connector.

Having said that, the motors charter can't be emphasised enough. If you think you know what you're doing, and don't know for certain - don't mess with your airbags. Ever.

langdang

Sorry, gofaster I can see you're being helpful here. I had myself braced for the "Health and Safety" high horses to come galloping in, and mistook you for one.

You're saying that static could generate a voltage on the triggering circuit for the airbag? I'll re-read the BMW TSB to see if there are any precautions, but is there you'd recommend? Battery disconnected was the only thing I thought I had to do?

The BMW TSB is 13pages with pictures, didn't want to post it verbatim.

langdang

PaintDoctor wrote: »

The correct way to do this, would be to continue to use BMW's connections, and on the cable between the floor and the first connector going up into the seat, cut it there (Battery disconnected, and everything grounded as much as possile, wrist straps, etc). Solder in an extension into this cable, and heatshrink all the wiring to make sure it is 110% insulated. This way you now have a longer cable, can disconnect the seat, and you're reducing the risk of the airbag deploying by not working on the seat, or it's connector.

Having said that, the motors charter can't be emphasised enough. If you think you know what you're doing, and don't know for certain - don't mess with your airbags. Ever.

I was hoping for your advice on this one!

Looks like this has been (pretty much) done by a previous owner or "agent thereof".
But they didn't do the S shaped bend around connectors and cable tie as described by the BMW TSB. This looks like a crucial part.
I'll insulate the existing crappy job and see if I have enough cable to mimic the new BMW recommended setup. Shur two more trips to have this reset won't hurt.

The BMW fix uses crimps AND connectors by the way.

gofaster_s13

langdang wrote: »

Sorry, gofaster I can see you're being helpful here. I had myself braced for the "Health and Safety" high horses to come galloping in, and mistook you for one.

You're saying that static could generate a voltage on the triggering circuit for the airbag? I'll re-read the BMW TSB to see if there are any precautions, but is there you'd recommend? Battery disconnected was the only thing I thought I had to do?

The BMW TSB is 13pages with pictures, didn't want to post it verbatim.

langdang wrote: »

Looks like this has been (pretty much) done by a previous owner or "agent thereof".
But they didn't do the S shaped bend around connectors and cable tie as described by the BMW TSB. This looks like a crucial part.
I'll insulate the existing crappy job and see if I have enough cable to mimic the new BMW recommended setup. Shur two more trips to have this reset won't hurt.

The BMW fix uses crimps AND connectors by the way. All I would have been doing is removing the most likely cause of a fault in the system.

It was health and safety advice but not the kind you were expecting;)

As regards crimping vs soldering, you are right, crimped connections should be used, the heat produced by soldering causes localised brittle/weak spots in the wiring which is why manufacturers always use crimped connectors.

Owen

langdang wrote: »

The BMW fix uses crimps AND connectors by the way. All I would have been doing is removing the most likely cause of a fault in the system.

The crimps in the BMW method are inside the connectors. I've seen enough of them done in the BMW garage I used to work in for the last 7 years. Crimps are fine for stereos and speakers (Even though I wouldn't use them). They're not fine for safety equipment.

Owen

gofaster_s13 wrote: »

As regards crimping vs soldering, you are right, crimped connections should be used, the heat produced by soldering causes localised brittle/weak spots in the wiring which is why manufacturers always use crimped connectors.

Soldering will produce a weak spot if you're bad at soldering. Crimping is fine for electronics, but not for safety equipment - especially the likes of a seat which is moving backwards and forwards.

If you need proof, crimp two wires together, and then start flexing the crimped cable where it meets the crimp. After about 20 minutes you'll feel it getting a lot easier to flex, and eventually, it'll come out. Do you really want something like that wired to the airbag in your seat which is moving forwards and backwards, and everytime someone hoovers under the seat and knocks the cable around too?

the merchant

I don't see any real concerns with carrying out this work yourself as long as you feel confident in your ability.

If OP had posted how to carry out a brake disc upgrade or something like that nobody would have said a word even though brakes are THE most important safety feature on a car.

I feel there should be more threads like this here without the "won't someone think of the children" brigade giving their 2 cents worth.

Owen

the merchant wrote: »

If OP had posted how to carry out a brake disc upgrade or something like that nobody would have said a word even though brakes are THE most important safety feature on a car.

Probably, because if you do a job on the brakes, you can test it afterwards and make sure it's fine. There's only one way to test an airbag

gofaster_s13

PaintDoctor wrote: »

The crimps in the BMW method are inside the connectors. I've seen enough of them done in the BMW garage I used to work in for the last 7 years. Crimps are fine for stereos and speakers (Even though I wouldn't use them). They're not fine for safety equipment.

Sorry, your right they shouldnt be used for safety equipment, imo Bmw should either bring out a lengthened bridge piece or a complete new section of loom. Again regarding crimps versus soldering, crimps are the better option as they don't put weaknesses into the wiring(try it yoursely with a solder joint in a piece of wire and a crimped joint, flex both repeatedly and see which lets go first;) ) If you get a custom loom made for a Race/rally car or custom looms in Ambulances fire engines etc, you will never find solder anywhere in them.

the merchant

PaintDoctor wrote: »

Probably, because if you do a job on the brakes, you can test it afterwards and make sure it's fine. There's only one way to test an airbag

That's right - by fitting dodgy brakes and hitting a tree on your test drive!

Owen

gofaster_s13 wrote: »

Sorry, your right they shouldnt be used for safety equipment, imo Bmw should either bring out a lengthened bridge piece or a complete new section of loom.

Agreed. This is a DIY fix though, and my method if someone was trying to DIY repair it, would be vastly stronger and safer than a crimp, and still keep the seat removable.

gofaster_s13 wrote: »

If you get a custom loom made for a Race/rally car or custom looms in Ambulances fire engines etc, you will never find solder anywhere in them.

Agreed too. Looms should be break free where possible. Any loom made from the ground up will have cable, connectors, and crimps inside the connectors where theyr'e anchored to prevent flexing. In fact, in a lot of BMW official retrofits, they will supply premade looms. The MFSW retrofit kit and heated seat retrofit kits I installed were more or less plug and play.

langdang

gofaster_s13 wrote: »

It was health and safety advice but not the kind you were expecting;)

As regards crimping vs soldering, you are right, crimped connections should be used, the heat produced by soldering causes localised brittle/weak spots in the wiring which is why manufacturers always use crimped connectors.

Ah yeah, but twas useful health and safety advice rather than the [BOOMING VOICE] THOU SHALT NOT[/BOOMING VOICE] type.

Glad I posted here, two things to consider - insurance and static.

And the eternal crimp versus solder debate;)
Either way the joining of two wires is going to be weaker than one continuous wire, but with a proper buttsplice and heatshrink I think it would be ok.
There a buttsplice mentioned in the BMW TSB, so there is crimping going on somewhere other than inside the connector.

DublinDilbert

gofaster_s13 wrote: »

Again regarding crimps versus soldering, crimps are the better option as they don't put weaknesses into the wiring(try it yoursely with a solder joint in a piece of wire and a crimped joint, flex both repeatedly and see which lets go first;) ) If you get a custom loom made for a Race/rally car or custom looms in Ambulances fire engines etc, you will never find solder anywhere in them.

I would use solder over a crimp any day of the week. There are some good crimping systems out there, but most people lack the correct crimping tools. Only people who specialise in making harness would have the equipment to correctly crimp the terminals on.

Any joint should always be supported and never allowed to flex. You can support the joint in a number of ways, cable tie the two wires together or just tie a not in them.

Owen

DublinDilbert wrote: »

I would use solder over a crimp any day of the week.

+1. Any when a soldered wire is correctly fitted with the right sized heat shrink, it becomes quite resistant to flexing.

galwaytt

A couple of things spring to mind:

1. The fail-safe situation in the design of the car is, in the event of a fault, to NOT fire the airbag, so having a fault in either BMW's wiring (which there is), or in yours, has the same net effect: the airbag won't fire.

2. As for the issue of using/not crimps - it really is moot. BMW connectors, are onlya barrel-crimped connection, but inside a plastic housing. And that is there for one reason: cost. It's cheaper to build the car using them. A standard red/yellow/blue oval crimp (á la Halfords etc) is not the same crimp. Go to Radionics/Farnell/Maplin and buy insulated open barrell crimps, use the proper crimper, and your work is no less than BMW's.

FWIW, a barrel crimp is a two-part crimp - the lower section, nearest the connection to the other component, crimps the connector only, the upper crimp, behind that, crimps the insulation, for strain relief. It is the only crimp I use, and you can get them anywhere. Even R/C toys use them on the charger plugs and sockets (about €2.5 in Maplin, actually, c/w both connectors AND the plastic housing).

You can see the two 'crimp areas' in this pic: - the 'triple-crown' area is for CONDUCTOR only, and the 'single crown' part is for the INSULATION only. (btw, these are Bosch connectors, ). Pulling the cable therefore, means you are not pulling on the electrical connection, but on the jacket.

gofaster_s13

galwaytt wrote: »

A couple of things spring to mind:

1. The fail-safe situation in the design of the car is, in the event of a fault, to NOT fire the airbag, so having a fault in either BMW's wiring (which there is), or in yours, has the same net effect: the airbag won't fire.

You can see the two 'crimp areas' in this pic: - the 'triple-crown' area is for CONDUCTOR only, and the 'single crown' part is for the INSULATION only. (btw, these are Bosch connectors, ). Pulling the cable therefore, means you are not pulling on the electrical connection, but on the jacket.

The failsafe is not to fire but the problem arises when somebody unqualified to work on airbags starts cutting and joining wires without properly discharging themselves of static and the vehicle of static, static can and does occasionally trigger airbags.

Those are the crimps we use when making or modifying looms, stronger and better than solder. No matter how good you are at soldering, the heat used will make copper wire or coppper alloy brittle.

breadmond

gofaster_s13 wrote: »

The failsafe is not to fire but the problem arises when somebody unqualified to work on airbags starts cutting and joining wires without properly discharging themselves of static and the vehicle of static, static can and does occasionally trigger airbags.

Those are the crimps we use when making or modifying looms, stronger and better than solder. No matter how good you are at soldering, the heat used will make copper wire or coppper alloy brittle.

the airbag will not fire because of static discharge because he has disconnected the battery. The wires he's working on are attatched to the occupancy sensor and will feed info to the airbag computer. As this computer has no power being supplied to it, it will not fire the airbag

langdang

Yes, those crimp on connectors are much better than the boggo blue/red types.
The butt splice ones used by BMW are more like that, ie separate crimping for conductor and insulation. I can't see anything as good as those Bosch ones in Maplin, will check out Farnell.


Breadmond, that was my thinking on it originally, no specific signal from the central control unit = no airbag firing. Worried now that static would cause a build of charge at the inputs to this computer that might cause a trigger when battery reconnect or ignition is turned??? Gofaster does seem to have knowledge in this area. So I'll take static precautions, wrist strap etc, and go have another cup of tea or two before I power up again?

Good info there boys, thanks so far.

langdang

Found some nice info here, including references to why static is an issue.
Cheers for the heads up gofaster, I would have assumed that any automotive components were even more static resistant than normal components. Seems not for airbags..

http://autospeed.com/cms/title_Airbag-Safety-Wiring-Repairs/A_3007/article.html

If I end up doing this I'll probably use the crimp butt splice connectors as pictured on that link. As long as I use a proper crimp tool, ie not the 5yoyo special most people have hanging around, then all should be good. Hinges on being able to find a decent crimp tool, but I reckon I can find one to borrow.

Again for anyone else having airbag warning light trouble and tempted to follow my example:
1) Don't.... unless you're confident you know what you're doing.
2) Don't.... unless you're sure it's a "connector under the seat" issue
3) Don't... well, not based on the info in this thread alone. I have a full step by step guide, specific to the car I'm working on.