Volvo RWD 700 Forum

INDEX FOR 10/2025(CURRENT) INDEX FOR 12/2022 700 INDEX

[<<]  [>>]


THREADED THREADED EXPANDED FLAT PRINT ALL
MESSAGES IN THIS THREAD




  REPLY TO THIS MESSAGE    PRINT   SAVE 

Airbag Clockspring/contact reel - shorted between wires? 700

I purchased a used clockspring after I broke mine and wanted to check it before I got too far along with it.

Totally out of the car and unhooked, the 2 terminals for incoming power read 0hms between each other. Does that seem right? I thought that the detonator was activated by flowing power between the two pins, not between both pins and ground.

700/900 clockspring. The part number is 3516420.

I can't find any kind of spec for the resistance between terminals nor from end to end. It is basically just a wire, but still it seems a little wrong.








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    Airbag Clockspring/contact reel - shorted between wires? 700

    Hi Will,

    Brickboard mail is busted here, and I got no email from you.
    Profiles is also busted where I have my email posted.

    I did find a Volvo SRS service manual for 1994 940/960 that offers a lot of info, much of it safety oriented, that should help.

    Bill








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    Airbag Clockspring/contact reel - shorted between wires? 700

    Hi Will,

    Brickboard mail is busted here, and I got no email from you.

    I did find a SRS service document for 1994 940/960 that might help with the
    1989 SRS schematic.

    Get a disposable email account use it once, and don't pretend there's any security on the web.

    Bill








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    Airbag Clockspring/contact reel - shorted between wires? 700

    To answer my own question, yes it's normal for there to be 0 resistance lead to lead. Seems like the design is to just run power on both wires and it grounds somehow.

    I pulled a 2nd one at the junkyard today for almost 50 bucks. It measures the same as the other one.








    •   REPLY TO THIS MESSAGE    PRINT   SAVE 

      Airbag Clockspring/contact reel - shorted between wires? 700

      The clockspring should be close to zero resistance end to end, but not between terminals. It would be rare to have it shorted internally. The day you don't have continuity through the clockspring is the day it's broken and needs to be replaced. The SRS lamp will light if it's unhappy seeing the airbag and the clockspring is broken or shorted. The SRS green manual can be found online with a bit of effort. DO NOT use a continuity or multimeter with the airbag connected! When re-installing the steering wheel the wheels need to be pointed straight ahead (!!) and the clockspring needs to be locked in the neutral position, which is mid-way to being wound tight then back it off rather than advance in order to engage the screw in the locking tab.
      --
      Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now








      •   REPLY TO THIS MESSAGE    PRINT   SAVE 

        Airbag Clockspring/contact reel - shorted between wires? 700

        End to end, I expected nearly 0 resistance, but pin 1 to pin 2, I expected an open. I think it just has 2 pins to have a reliable path to ground. Seems strange to me, but I haven't seen a wiring diagram to the actual airbag.

        Maybe my meter is also bugging out. I need to put a new 9V in my good meter, and I didn't manage to do that before I left. Just in case, I bought a spare airbag too. Maybe they'll both end up on ebay.








        •   REPLY TO THIS MESSAGE    PRINT   SAVE 

          Airbag Clockspring/contact reel - shorted between wires? 700

          Hi Will,

          2nd attempt to post this.

          I have the schematic and component location for SRS/Air bag
          out of the 1989 740 wiring manual TP 31383/1.
          What's your email, I'll scan it and send it to you.

          Take care with that fragile coil spring, Bill








          •   REPLY TO THIS MESSAGE    PRINT   SAVE 

            Airbag Clockspring/contact reel - shorted between wires? 700

            Hey, Bill.

            Sounds good to me. I think I'm set for now, but I emailed an old address I have for you if you want to send it again.

            The mail button next to my name seems like it may work.

            I'll be gentle with it, but mostly I need to be mindful of its rotation position.

            Will








        •   REPLY TO THIS MESSAGE    PRINT   SAVE 

          Airbag Clockspring/contact reel - shorted between wires? 700

          Turns out what you're seeing is correct and that used clockspring is likely perfectly okay. It's been so many years, I'd forgotten about this until just now. There's a spring wire shunt in one of the clockspring connectors. When it's disconnected the shunt closes and shorts the connector pins. I vaguely recall it was in the upper airbag connector, but the steering column connector may also have one, also the airbag connector itself. If you examine them carefully you can see the shunt. The shunt is there primarily for safety reasons to prevent static discharge or voltage from a meter getting into the circuitry and causing an airbag to discharge or damage the controller electronics.

          Note that the shunt needs to be taken into account when trying to test the clockspring with a meter. If you put your meter on the shunted pins it will be seeing the shunt, not the wiring up to the other connector. On the plus side, when the clockspring breaks, both circuits are interrupted. On the negative side, the broken area may short at the break. The proper way to test a clockspring is to use your meter on two pins that aren't shunted with the other end shunted (or jumpered). If the meter doesn't see any continuity (up to 2 or so Ohms is normal) then it's broken. You then rotate the clockspring and if the resistance changes then you know tge spring is broken. You can often see the break through the clear plastic.

          The green electrical manual for any year 940 will have the SRS wiring and likely also some indication which connectors have the shunts.
          --
          Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now








          •   REPLY TO THIS MESSAGE    PRINT   SAVE 

            Airbag Clockspring/contact reel - shorted between wires? 700

            Aha! That would explain it. I see the shunt but thought it was part of 2 individual strange terminals. They seemed like spring clips to keep them in good contact with the terminals from plug to plug.

            There is definitely a shunt at the connector into the clockspring. Thank you!

            I'll post the measured values for the clockspring with the shunt disabled.








            •   REPLY TO THIS MESSAGE    PRINT   SAVE 

              Airbag Clockspring/contact reel - shorted between wires? 700

              You're welcome. Glad I finally remembered that. Looking at the green manual wiring diagrams for the SRS system, it appears there are spring wire shunts in every orange connection between the airbags and the controller, except at the controller connector itself. As this is a safety mechanism it makes sense to do it everywhere.
              --
              Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now







<< < > >>



©Jarrod Stenberg 1997-2022. All material except where indicated.


All participants agree to these terms.

Brickboard.com is not affiliated with nor sponsored by AB Volvo, Volvo Car Corporation, Volvo Cars of North America, Inc. or Ford Motor Company. Brickboard.com is a Volvo owner/enthusiast site, similar to a club, and does not intend to pose as an official Volvo site. The official Volvo site can be found here.