Every guide to working on your car says to “disconnect the negative battery terminal”, lest your airbag exploded and kill you if you connect the red to the black when trying to install a new stereo. Is this purely CYA territory or is this a real danger / has actually happened once or twice. It seems to me that even if you’re actually messing with the airbag connectors to say install a heated seat element or pull the steering wheel, you’re not going to short it.
The only thing remotely similar I’ve been able to turn up is the case of a guy that was installing a steering wheel controlled anti-theft system, and for whatever reason disassembled the clock spring and then repacked it back together incorrectly, resulting in the wires rubbing together and eventually shorting.
I did a very brief google search and found a youtube video where the airbags were accidentally deployed while the user was trying to troubleshoot a wiring issue and hadn’t disconnected the battery. The person working on the car lifted up the airbag module which made it think that the car had rolled over and automatically deployed the airbags. The actual video was a recreation of an event that had happened to a friend of his.
I also found a news item from 2016 where Honda confirmed that a man was killed while working on a Honda vehicle with the battery connected and the key in the ON position. That particular airbag had been recalled due to safety issues and could spray out deadly fragments when deployed. It is also important to note that the man was using a hammer at the time, though it’s not clear exactly what he was doing with it. Honda was not sure if the man’s death had been caused by fragments from the defective airbag or by “interaction of the hammer with the deploying airbag”. Honda also wasn’t sure exactly what had caused the airbag to deploy, though they did note that there were a lot of deceleration sensors in the area where the man was working.
I don’t think it would be common, but as an electrical engineer I can picture a few scenarios where working on the car’s wiring could cause a potential short and trigger the airbag.
And, I mean… think about it this way: The things are a safety feature that intentionally have a hair trigger (under certain specific conditions). If nothing else — even if nobody is anywhere near the thing, and there’s no personal danger — just consider how expensive an accidental deployment would be. Resetting an airbag isn’t just a matter of squishing it back into the steering wheel.
Disconnecting it takes mere seconds, and ensures you don’t have to try and figure the odds on various accidental deployment scenarios. “Never tell me the odds!”
I just txted with a friend of mine. He owns a BMW + other exotics repair shop. Got a dozen guys wrenching for him, plus a bigger body shop. He’s been in the biz about 20 years either on his own or before that as a tech at BMW or Merc dealers. IOW, an expert in his field.
I said:
You ever heard of or seen somebody fire an airbag accidentlay during other maintenance?
He said:
Yes.
If the ignition is off it is hard to do …
But sometimes guys have left the ignition on while working on the car and – BOOM
For example, I knew a tech who came to the BMW dealer I worked at. He’d come from a Ford dealer. He was working on a BMW 3-series convertible. He had the center console out of the vehicle. Then he unbolted the ACSM (Advanced Crash Safety Module) that lives under the console. He was working in that area so he flipped it over to get it out of his way (it was still connected).
Well, that contains the gyroscope that detects rollover. Blew every airbag in the car. The side airbag struck him with such force he had a bruise of 2 square feet. He was a big fat dude.
The biggest concern is working on the clock spring on the steering column. The mechanic is working extremely close to the air bag.
Eric on South Main Auto YT channel often comments about his concerns. Unfortunately clock springs fail and require replacing. He’s posted several repair videos.
***The clock spring is a steering wheel sensor. Tells the computer how to turn the .
There’s something to be said for making good habits and generally accepted standards and workmanlike procedures and all that stuff. Sometimes it isn’t so much the odds of something happening that are so much a concern as it is the consequences if it does. Like air bags blowing up in your face.
You’d be amazed at how many people used to unbolt the driveshaft on rear wheel drive cars and trucks, while underneath, on a steep driveway. By all accounts it is not fun. They just weren’t thinking things through. Getting in a hurry is another great way to make boneheaded mistakes.
The wheel angle sensor is separate to the clockspring, although they may be combined into the one physical unit - and even if separate units, often sold as a combined spare part. The clockspring is the mechanism by which all the connections from the various switches and the airbag in the steering wheel reach the car, allowing for steering wheel rotation. So in addition the the airbag, horn, often cruise control, flappy paddle switches, audio system control etc. Rather than slip rings for each connection, a springy flexible conductor bundle is wrapped multiple times inside the unit, and encircles the steering column. It looks a lot like the mainspring of a clock. They fail because of fatigue after many many flexes as the steering wheel is rotated.
Any or all of the functions fail as the clockspring connections break. They are not cheap to replace. Loss of horn or airbag control is not a happy result. Since it directly connects to the airbag, all the caveats apply to safely working on it.
Tangentially, (hah! that’s kind of a pun, actually; read on…) electronics components that have to move relative to each other linearly are often connected together in somewhat similar manner, via a length of ribbon cable long enough to span the maximum separation distance between the two endpoints. The cable is then allowed to curl up into a void above the connection, when the two ends are moved closer together.
I had a mobile phone with a slide-out physical keyboard,1 where the keyboard module connected to the main body using just such a cable. There had to be a good 40-50 incredibly thin wires all lined up inside this flat, [not-]flexy[-enough] bit of ribbon… which ended up shearing apart across nearly half of those wires, right at the point where it folded the tightest when the keyboard was retracted. Just from all the repeated flexing and unflexing. This occurred far earlier in the phone’s lifetime than one would have reasonably expected such a device to last.
I may hate touchscreen keyboards, but I’ll be the first to admit that the fewer mechanical parts you have on a device — especially something portable/heavily-interactive like a phone — the longer it tends to last. Some form of mechanical failure was the ultimate demise of every phone I’d ever owned, in the pre-“slab-with-a-flat-glass-screen-on-one-face” times.
Now, it’s been replaced by battery swelling. Cause of death for four of my last five phones. (The fifth, I dropped face-down onto a ceramic toilet rim. The screen protector did a stellar job of preventing the many, many dozens of screen-shards from departing the phone body, but that’s about it.)
Notes
(In fact, I owned the very last such model that was released for the consumer market, before physical keyboards became completely extinct — not counting Blackberry. Because I was a die-hard, and [still] loathe the comparatively unsatisfying experience of typing on a virtual keyboard that I have to look at in order to use. Whereas with a physical keyboard, it didn’t take me long to reach the point where I could touch-type with my thumbs.)
The printhead on a typical inkjet is tethered with exactly that sort of cable. The good news is the space constraints aren’t so tight inside a printer, so cable failures there are mercifully rare.
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