What is this tiny severed wire against the firewall?

elliswyatt · 04-07-2019, 04:58 PM

Checking under the hood prior to a Sunday drive and found this wire that has broken or been cut. The long piece comes off of the battery terminal, the short piece towards the top of the photo is from the cable bundle. What is it and could it be the reason why I suddenly have an airbag warning light?

Clearancediver · 04-08-2019, 10:58 AM

I believe that is what is called the B+ wire that is part of the SRS system. I would definitely rejoin those wires with a properly soldered join covered with heat shrink.

You will need to clear the error code it generated afterwards.

Huz-Z · 04-08-2019, 11:13 AM

I would think that a section of wiring like that would be considered a critical part of the car's occupant safety system and that its' housing and routing through the car would be robust and designed to protect it from inadvertent damage.

Michael9218 · 04-08-2019, 01:47 PM

Now I had thought that was a power wire to the ECU to provide power when the car is shut off.

This wouldn't explain your SRS light...

JCF · 04-08-2019, 03:53 PM

Could it be a part of the alarm system? While it may not have an alarm, they were wired for them.

elliswyatt · 04-08-2019, 05:54 PM

Quote:

Originally Posted by Michael9218

Now I had thought that was a power wire to the ECU to provide power when the car is shut off.

This wouldn't explain your SRS light...

If your explanation is correct, would there be other noticeable symptoms of an unpowered ECU after shut off?

Michael9218 · 04-08-2019, 07:46 PM

Yes, it can throw eroneous codes.
I have a battery cutoff switch in my track car and was getting odd codes. Was told by tuner to let the ECU have power for several minutes after engine shut down before cutting battery. Curied the odd codes.
Reconnect that wire, reset the SRS light and see if this solves your issue.

04-07-2019, 04:58 PM	#1
elliswyatt Private First Class 70 Rep 110 Posts Drives: 2021 M240i 6MT, 2016 Mk7 GTI Join Date: Oct 2018 Location: St. Louis, Missouri iTrader: (0)	What is this tiny severed wire against the firewall? Checking under the hood prior to a Sunday drive and found this wire that has broken or been cut. The long piece comes off of the battery terminal, the short piece towards the top of the photo is from the cable bundle. What is it and could it be the reason why I suddenly have an airbag warning light? Attached Images __________________ www.coldwartourist.com
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04-08-2019, 10:58 AM	#2
Clearancediver Lieutenant 93 Rep 411 Posts Drives: 2004 Z4 Join Date: Oct 2012 Location: Victoria, BC Canada iTrader: (0)	I believe that is what is called the B+ wire that is part of the SRS system. I would definitely rejoin those wires with a properly soldered join covered with heat shrink. You will need to clear the error code it generated afterwards. __________________ Sent from my smart phone...
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04-08-2019, 11:13 AM	#3
Huz-Z Brigadier General 851 Rep 4,057 Posts Drives: Z4 3.0si, 328 XDrive, X5 35i Join Date: Aug 2009 Location: Canada iTrader: (0)	I would think that a section of wiring like that would be considered a critical part of the car's occupant safety system and that its' housing and routing through the car would be robust and designed to protect it from inadvertent damage. __________________ Huz-Z BMW Z4 3.0si Roadster. Montego Blue Metallic. Premium and Sport Package.
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04-08-2019, 01:47 PM	#4
Michael9218 Lieutenant 595 Rep 484 Posts Drives: 2007 Z4 M Coupe Join Date: Oct 2012 Location: Woodstock, GA iTrader: (0)	Now I had thought that was a power wire to the ECU to provide power when the car is shut off. This wouldn't explain your SRS light...
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04-08-2019, 03:53 PM	#5
JCF Second Lieutenant 32 Rep 218 Posts Drives: 07 Z4 M Coupe Join Date: Jan 2015 Location: Charlotte, NC iTrader: (0)	Could it be a part of the alarm system? While it may not have an alarm, they were wired for them. __________________ /// LED Lighting /// Pedal Haus M aluminum pedals and heel plate /// BMW logo puddle lights /// CF wrapped console /// LeatherZ MK4 console storage, armrests, door pulls /// ZHP illuminated shift knob /// BMW under seat storage /// Soundplicity III /// Stubby Antenna /// Eventuri Intake /// Tekcarbon CF valve cover /// Stromung exhaust /// Rogue Engineering Transmission Mounts ///3rd brake light blinker
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04-08-2019, 07:46 PM	#7
Michael9218 Lieutenant 595 Rep 484 Posts Drives: 2007 Z4 M Coupe Join Date: Oct 2012 Location: Woodstock, GA iTrader: (0)	Yes, it can throw eroneous codes. I have a battery cutoff switch in my track car and was getting odd codes. Was told by tuner to let the ECU have power for several minutes after engine shut down before cutting battery. Curied the odd codes. Reconnect that wire, reset the SRS light and see if this solves your issue.
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