Automotive repair expert Brad Bergholdt answers readers' FAQs. Today, he addresses a problem with the horn that leads to a problem with the driver-side airbag. The culprit: a device called a cable reel that holds all the steering-wheel wiring.
Q: I have a ’99 Corvette. My horn would not work with the steering wheel in the straight-forward position. If I turned it all the way to the right or left, the horn would work. I turned the wheel all the way to the left and pushed on the horn, as it was blowing, I turned it all the way to the right while pressing the horn and it continued to blow. I then turned it all the way back to the left while it was still blowing. Now the horn works with the steering wheel in any position. But now the airbag deploy light stays on. What do you think happened?
A: This a great question, and if I may admit relief, an easy one.
For many years the electrical connection making a steering-wheel horn switch possible was a spring-loaded contact button and brass slip ring. The button was attached to the steering column and the ring was on the back side of the steering-wheel hub. As you turned the steering wheel, the button would slide across the ring, making a fairly reliable (but occasionally squeaky) connection.
When SRS (supplemental restraint systems — or airbags) came along, a more positive electrical connection was needed between the steering column and the airbag, mounted within the steering wheel. This device is known as a cable reel — or, informally, a clock spring.
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Imagine a ribbon cable: a flat, firm plastic tape containing a half-dozen or more wires embedded side by side, wound into a tape-measure-like assembly. One end of the cable connects to the steering column and the other to the steering wheel.
As the steering wheel turns, the ribbon cable slips and slides, winding and unwinding within a plastic housing. The airbag requires only two of the wires, the others are for the horn or other steering-wheel switches.
Cable reels haven’t proven to be absolutely reliable. There have been more-than-occasional complaints of crunching noises, an inoperative horn and illuminated SRS lamps.
It sounds like one or more conductors in your cable reel (the horn circuit) began to separate, and after a lock-to-lock turn of the steering wheel, the ribbon cable twisted just right to create a new symptom. The SRS system monitors the electrical loop passing to, through and from the airbag and alerts you, via the warning lamp, if trouble occurs. Through no fault of yours, the cable reel now requires replacement.
Renewing a cable reel isn’t a difficult job, but it’s imperative that SRS service safety precautions be followed. Airbags can cause serious personal injury should they accidentally deploy during service.
Also, it’s important that the new cable reel be properly centered relative to steering shaft position. An improperly installed cable reel will break with the first sharp U-turn.
E-mail Brad Bergholdt at firstname.lastname@example.org. Sorry, no personal replies.