Help required please - battery safety terminal fault and airbag warning light

[BMWZ4MC]

My airbag warning light is illuminated and cannot be reset. I have an error code for a fault with the battery safety terminal (the pyrotechnic battery shut off device that is triggered by an impact).
Whilst investigating, I found that a wire has pulled out of a plug in a small cable that connects to the pyrotechnic charge. I presume this cable allows the SRS module to monitor the integrity of the battery safety terminal and perhaps even deploy the charge. The plug allows the BST to be disconnected from the car; the faulty wire has pulled out of the loom side of this plug.
As a result of a previous battery leak whilst my car was in transit from the UK to Australia, the plug has corroded and the two halves are inseparable. Damage from corrosion is also the likely the cause of the wire separating from the plug.
I’d be very grateful if someone could post a photograph of an intact plug and the wires either side of the plug please. The part is M-specific.

This is the cable in question:


The broken wire (red arrow) should be in the plug (green arrow):


This is my corroded plug:


Many thanks.

 

[colb]

Bad case of the crusty's on that plug and severed wire, a good clean with Deox electrical cleaner and cut back to clean copper on the severed cable should be achievable if the pins in the socket have survived, if not then you should be able to get a replacement from BMW or one of the breakers of Z4's. You could also put an after market pair of connectors in there to make good, its only a two pole plug and socket.
Hopefully when connection is restored you need to clear the code with a scan tool once cleared any airbag light that is showing should go out as long as the connection has been made good.

 

[BMWZ4MC]

Hi Col, thanks for the reply. The plug and socket are inseparable and I’m not sure which of the six holes in the loom sided plug the wire came from. I’m happy to cut out the plug and splice the wires together, but I’m looking for clues as to which wires belong together.
That particular BST is unique to the Z4M. There were only around 100 sold in Australia, so finding anything in a breakers yard here is impossible!

 

[Smartbear]

Hi Col, thanks for the reply. The plug and socket are inseparable and I’m not sure which of the six holes in the loom sided plug the wire came from. I’m happy to cut out the plug and splice the wires together, but I’m looking for clues as to which wires belong together.
That particular BST is unique to the Z4M. There were only around 100 sold in Australia, so finding anything in a breakers yard here is impossible!

A multimeter set to continuity/buzzer should prove which wire belongs to which.
Rob

 

[DevonPaul]

That particular BST is unique to the Z4M. There were only around 100 sold in Australia, so finding anything in a breakers yard here is impossible!

If you can find one in the UK, we have some friends over from Oz next weekend who could take it back with them. Gary wouldn't mind, a bit of a car guy and last visit they took a Merc CLK back with them, although he does look down a bit on the Z4 and tends to regard anything under 5 litres as a lawnmower engine.

 

[grannyknot]

Here you go, it just arrived. I have that same code but in my case the original cable is in perfect working order but can't clear the code so I bought a new one, maybe it will work.
I can't get a pic of the connector on the cars harness until tomorrow.

 

[GT Spec]

The replacement battery cable from BMW is PN# 61127841239

 

[BMWZ4MC]

That particular BST is unique to the Z4M. There were only around 100 sold in Australia, so finding anything in a breakers yard here is impossible!

If you can find one in the UK, we have some friends over from Oz next weekend who could take it back with them. Gary wouldn't mind, a bit of a car guy and last visit they took a Merc CLK back with them, although he does look down a bit on the Z4 and tends to regard anything under 5 litres as a lawnmower engine.

Thanks for the offer, much appreciated. I’m pretty sure the BST is good and it’s the connection to the loom that is the problem, so I’m going to try to fix that first.

 

[BMWZ4MC]

The replacement battery cable from BMW is PN# 61127841239

Cheers, and it’s horrendously expensive!

 

[BMWZ4MC]

Here you go, it just arrived. I have that same code but in my case the original cable is in perfect working order but can't clear the code so I bought a new one, maybe it will work.
I can't get a pic of the connector on the cars harness until tomorrow.

Thanks granny! That’s exactly what I need. Similar pics of the black plug on the loom side of the connection should give me the information I need.

 

[Wassup]

hI bmwz4mc, sorry to hear the issues you're having with the bst cable/wiring. If you can't get it too work with a repair, I have the wiring loom from my Z4M that I parted out last year. Let me know if you need that portion of the loom

 

[BMWZ4MC]

Thanks Wassup. I’ll let you know if I can’t fix it

 

[BMWZ4MC]

It transpired that it was extremely easy to fix. Firstly, I stripped back the insulation of the three intact wires adjacent to the inseparable plug and socket, and measured the resistance between each of the black wires and the intact brown/red wire with everything in situ. However, both of the black wires were in continuity with the intact brown/red wire (presumably through the loom), so that didn't clarify which wires made up each pair.
Next, I labelled one of the black wires and cut both black wires as well as the brown/red wire adjacent to the plug and socket. Isolated from the loom, it was possible to establish which black wire was in continuity with the brown/red wire through the plug and socket. I then used a two-gang terminal block to connect the corresponding black wire with the brown/red wire and to connect the other black wire to the brown wire. Lastly, I fashioned a plastic box from an old coaxial skirting board socket to contain the union and electrically isolate it.
Once I'd cleared the code, the SRS light went out and all was well...except for the ongoing overheating issue and the large stone chip in the windscreen that will fail the safety check in November!
Thanks all for your help

 

[colb]

Great fix glad you got it sorted, airbag lights are the worst thing on these cars to get right and sadly quite a frequent occurrence across the model range. Airbag modules are the work of the Devil.