Simple Trick for Clock Spring Continuity Check
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Joined: Jan 2007
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From: Austin, TX
Simple Trick for Clock Spring Continuity Check
Facing the dreaded airbag light and fault code 21, I read through all the threads on this forum and did the following:
The airbag-side of the under-dash connector has spring loaded shorting bars, so when the connector is unplugged the two pins are connected. This is a safety feature designed so that if voltage hits one of the pins it just shorts to the other pin rather than triggering the airbag. (There is a shorting bar in the airbag itself. I initially got zero resistance on the airbag. I then pushed the shorting bar away from one pin and got 2.3 ohms through the airbag.)
Here is the simple trick… Because the under-dash airbag connector is shorted when disconnected, you can check continuity of both legs of the clock spring by checking the resistance across the two sockets in the yellow connector that plugs into the airbag. (I cut 1” lengths of paper clips to slide into the sockets because my DVM probes were too large.) There should be continuity from one socket in the yellow connector, through the clock spring, across the shorted under-dash airbag connector, back through the clock spring and finally to the other yellow connector socket.
In my case there was no continuity, which meant I had a bad clock spring. I wish I had done this test first!
I pulled the clock spring and opened it up, thinking I might locate and repair the broken wire. I found the broken wires in the ribbon near the connector, but decided that the repair was beyond my skill set.
I ordered a new clock spring from Sunset for $228. Problem solved.
- Check and clean grounds and connections
- Pull clock and re-soldered the joints.
- Disconnect battery (wait several minutes)
- Pull airbag and steering wheel
- Remove the plastic covers around the steering column stalks
- Follow the wires from the clock spring into the dash and locate the airbag connector – green/blue and green/red wires.
- Disconnect the under-dash airbag connector.
The airbag-side of the under-dash connector has spring loaded shorting bars, so when the connector is unplugged the two pins are connected. This is a safety feature designed so that if voltage hits one of the pins it just shorts to the other pin rather than triggering the airbag. (There is a shorting bar in the airbag itself. I initially got zero resistance on the airbag. I then pushed the shorting bar away from one pin and got 2.3 ohms through the airbag.)
Here is the simple trick… Because the under-dash airbag connector is shorted when disconnected, you can check continuity of both legs of the clock spring by checking the resistance across the two sockets in the yellow connector that plugs into the airbag. (I cut 1” lengths of paper clips to slide into the sockets because my DVM probes were too large.) There should be continuity from one socket in the yellow connector, through the clock spring, across the shorted under-dash airbag connector, back through the clock spring and finally to the other yellow connector socket.
In my case there was no continuity, which meant I had a bad clock spring. I wish I had done this test first!
I pulled the clock spring and opened it up, thinking I might locate and repair the broken wire. I found the broken wires in the ribbon near the connector, but decided that the repair was beyond my skill set.
I ordered a new clock spring from Sunset for $228. Problem solved.
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Nicely done & thanks for posting. This will come up during folks checking for an air bag issue. I have never heard of a clock spring going bad. Good to know.
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From: Austin, TX
They look like that. One is red and one orange.
I cannot remember which is which. The one with brown wires is for the horn and the other is for the airbag.
To get to it the other way, remove the steering wheel. This exposes a face plate. Remove the four screws from the face plate. Remove one screw from each side of the stalk cover (right near the joint). The frees the top half of the stalk cover. Mine required a bit of jiggling, but it came out easily.
I cannot remember which is which. The one with brown wires is for the horn and the other is for the airbag.
To get to it the other way, remove the steering wheel. This exposes a face plate. Remove the four screws from the face plate. Remove one screw from each side of the stalk cover (right near the joint). The frees the top half of the stalk cover. Mine required a bit of jiggling, but it came out easily.
Last edited by rwestervelt; Sep 28, 2018 at 07:14 PM. Reason: adding information
Racer
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Posts: 257
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From: Montana
Thank you for the help. It appears as though my clock spring is good but the airbag is bad as it didn't have any resistance across the circuit. Will try a 2.8 ohm resistor and try to reset the airbag light and see if that works.
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Instructor
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From: Austin, TX
Resistance Across Airbag
Before testing airbag resistance, use a toothpick to push the shorting bar away from one of the male connectors on the airbag. If you skip this step, the resistance will read zero because the two pins are shorted when the connector is unplugged.
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Facing the dreaded airbag light and fault code 21, I read through all the threads on this forum and did the following:
The airbag-side of the under-dash connector has spring loaded shorting bars, so when the connector is unplugged the two pins are connected. This is a safety feature designed so that if voltage hits one of the pins it just shorts to the other pin rather than triggering the airbag. (There is a shorting bar in the airbag itself. I initially got zero resistance on the airbag. I then pushed the shorting bar away from one pin and got 2.3 ohms through the airbag.)
Here is the simple trick… Because the under-dash airbag connector is shorted when disconnected, you can check continuity of both legs of the clock spring by checking the resistance across the two sockets in the yellow connector that plugs into the airbag. (I cut 1” lengths of paper clips to slide into the sockets because my DVM probes were too large.) There should be continuity from one socket in the yellow connector, through the clock spring, across the shorted under-dash airbag connector, back through the clock spring and finally to the other yellow connector socket.
In my case there was no continuity, which meant I had a bad clock spring. I wish I had done this test first!
I pulled the clock spring and opened it up, thinking I might locate and repair the broken wire. I found the broken wires in the ribbon near the connector, but decided that the repair was beyond my skill set.
I ordered a new clock spring from Sunset for $228. Problem solved.
- Check and clean grounds and connections
- Pull clock and re-soldered the joints.
- Disconnect battery (wait several minutes)
- Pull airbag and steering wheel
- Remove the plastic covers around the steering column stalks
- Follow the wires from the clock spring into the dash and locate the airbag connector – green/blue and green/red wires.
- Disconnect the under-dash airbag connector.
The airbag-side of the under-dash connector has spring loaded shorting bars, so when the connector is unplugged the two pins are connected. This is a safety feature designed so that if voltage hits one of the pins it just shorts to the other pin rather than triggering the airbag. (There is a shorting bar in the airbag itself. I initially got zero resistance on the airbag. I then pushed the shorting bar away from one pin and got 2.3 ohms through the airbag.)
Here is the simple trick… Because the under-dash airbag connector is shorted when disconnected, you can check continuity of both legs of the clock spring by checking the resistance across the two sockets in the yellow connector that plugs into the airbag. (I cut 1” lengths of paper clips to slide into the sockets because my DVM probes were too large.) There should be continuity from one socket in the yellow connector, through the clock spring, across the shorted under-dash airbag connector, back through the clock spring and finally to the other yellow connector socket.
In my case there was no continuity, which meant I had a bad clock spring. I wish I had done this test first!
I pulled the clock spring and opened it up, thinking I might locate and repair the broken wire. I found the broken wires in the ribbon near the connector, but decided that the repair was beyond my skill set.
I ordered a new clock spring from Sunset for $228. Problem solved.
thank you for this very helpful thread. Sorry to re-open this discussion but I have the same problem on my car. Unfortunatly, the clock spring seems to be good on my side as there is continuity between the two pins on the under-dasch airbag connector. What are the other things to be tested and how?
thank you.
best regards.
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Hi R Westervelt,
Nice write-up, I was unaware of the shorting-out safety feature. When replacing the steering rack on my car I sheared off the pins on the clock spring that tie it to the back of the steering wheel. I was able to fix the pins using a little cement and fishtank tube reinforcement. Also on my car the crazy over-engineered rotation lock on the spring unit was all gnarled up and broken and I found that removing it and just using some electrical tape to achieve the same function and then pulling off the tape once the steering wheel was in place was a very good low-tech alternative.
https://993servicerepair.blogspot.co...ck-on-993.html
Andy
Nice write-up, I was unaware of the shorting-out safety feature. When replacing the steering rack on my car I sheared off the pins on the clock spring that tie it to the back of the steering wheel. I was able to fix the pins using a little cement and fishtank tube reinforcement. Also on my car the crazy over-engineered rotation lock on the spring unit was all gnarled up and broken and I found that removing it and just using some electrical tape to achieve the same function and then pulling off the tape once the steering wheel was in place was a very good low-tech alternative.
https://993servicerepair.blogspot.co...ck-on-993.html
Andy