How much voltage to deploy airb ag?

dr.fuzzenstein

I have sitting on my desk the driver's side airbag from an 02 Polo.
The car in question has an airbag light on and the codes seem to point towards the driver's side airbag.
I have already replaced the clock spring (which was faulty), but the warning light remains.
I now want to measure the airbag with a mulitmeter as per this Youtube video:

https://www.youtube.com/watch?v=uAklUlvAIrs

I just trust nothing on the internet.

ZENER

Would this be any use to your fault-finding endeavors ?

Airbags are dangerous things to be fiddling with if you're not careful or not sure what you're doing. DEFINITELY DO NOT APPLY ANY VOLTAGE TO ANY OF THE TERMINALS !!! Digital Multimeters will only present a very small voltage on the test leads to measure resistance but this is not always the case with some cheaper ones or Moving Coil types (the $10 meter shown in that video for example).

Ken

dr.fuzzenstein

ZENER wrote: »

Would this be any use to your fault-finding endeavors ?

Airbags are dangerous things to be fiddling with if you're not careful or not sure what you're doing. DEFINITELY DO NOT APPLY ANY VOLTAGE TO ANY OF THE TERMINALS !!! Digital Multimeters will only present a very small voltage on the test leads to measure resistance but this is not always the case with some cheaper ones or Moving Coil types (the $10 meter shown in that video for example).

Ken

I've read that thread, not much in there.
The error code is N95, Airbag ignitor driver's side, faulty coil spring, slip ring, ignitor, and so on.
I have tested and replaced everything except the airbag itself and I'm not going to spend a minimum of E80 on a second hand airbag that could also be faulty.
The meter I'm using is a Meterman DM73B:



So it's not a cheap piece of crap.
As for the video itself, would anyone think what they're doing is dangerous?
You can find almost any type of information on the internet, except exactly what type of voltage and ampage deploys an airbag, then it all goes fuzzy and wishy washy, with the clearest answer I could find as "some voltage".
Not a great help.

langdang

Last time I asked here for advice about airbag stuff, an ex poster (gofaster_s13 ?) who worked in a garage said they were very sensitive to static. So wear a wrist band or ground yourself off a rad or sink before you go messing. (Don't wear a fleece while breakdancing on some carpet)

I'd have a lash off it, if it was my car. I'd probably wear some safety glasses and I wouldn't do it without someone around the place. Probably be fine, but if it goes wrong that thing is going to turn into a little missile, who knows where it's gonna go!

dr.fuzzenstein

I will look into attaching some wires onto the airbag and being as far away from it as possible as I measure it.
I'd like some Mythbuster's style blast-proof glass to be behind, because I like my body very much (it's not pretty but it gets me around) and would like to keep it in one piece!:D;)

langdang

Connecting wires and everything else will be as much hassle and as likely to cause problems as just measuring it. (Unless you mean strapping it down somehow, and not wires to do the measurement at a distance?) Just be careful. Take ESD precautions. Have steady hands. It's most likely (IMO) to be safe as long as those shorting bars mentioned in the video are pressed onto the pins. The risk of triggering it occurs when the shorting bars are moved away to make a measurement. (This is based purely on my interpretation of the video, and how I would design the system)

BTW, I basing the "probably be fine" on the fact that you've successfully tested the other stuff and gotten the airbag out of the car already without mishap. It's not something I'd advise everyone to have a lash off.

I reckon you'll be fine OP, but for the sake of anyone who finds this down the road in a search - stop and have a good think.
There was a guy on here recently who couldn't figure out why he couldn't read current by connecting the probes in parallel with the battery. Don't know if he even swapped terminals on the meter.

dr.fuzzenstein

Hahaha, don't worry, no probes connected in parallel with the battery here!:D
I actually have removed the airbag, it is sitting right beside me on my desk at the moment.
I had to remove the steering wheel in order to repair a faulty wiper stalk, another typical Polo malady, I found out that the actuator for the window washer system doesn't return to it's home position, causing your wipers to run continuously.
Removing the airbag from the steering wheel was a HUGE pain in the ass, btw.
All I can say is that a crowbar was involved and the original steering wheel looks more like a pretzel now.

dr.fuzzenstein

Right, I just went ahead and measured it anyway.
Firstly you have to bend away the grounding plates that create a short across the terminals.
Then, (wearing my trusty ESD wrist strap) I applied the probes of the multimeter to either one of the terminals and the metal ring that forms the grounding plates.
As expected, I got an open circuit. If you just measure the terminals without bending the grounding plates, you will just get a short.
After bending the grounding plates, and checking that there was no contact between the terminals and the grounding plates, I could get down to the business of actually measuring across the terminals.
As I expected, the resulting BOOM, MASSIVE EXPLOSION!, happened in the exact same way the Mayan Apocalypse did, i.e. not at all.
I got a nice, straight 2.0 Ohms across the terminals, suggesting that this particular airbag is still good to go.
A friend will help me reset the error codes and we're hoping that will clear the problem.
Because I'm selling that Polo at the moment and selling a car without an NCT is hard enough, but with faulty wipers and an airbag light on top of it? Not gonna happen.

ZENER

Did you reset the warning light via the OBD terminal?

dr.fuzzenstein

ZENER wrote: »

Did you reset the warning light via the OBD terminal?

It had been reset before via a VW OBD tool, but since then more work had been carried out that meant removing the airbag and steering wheel.
Will bring the car over to a friend who has the necessary tools, we will reset and see what happens.

dr.fuzzenstein

Right, just in case anyone is still reading this:
Brought the car over to a friend and he reset the airbag error codes.
Airbag light has stayed off since then, so all is well.
All for a total outlay of €40 for a secondhand clockspring, none too shabby for clearing an airbag fault methinks...