What does the coil spring do in a car?
What does the clock spring do in a car?
The clock spring (also called a slip ring or airbag clock spring) establishes the electrical connection between the rotating steering wheel and the fixed steering column. It transmits the ignition signal for the driver's airbag and ensures that the horn, steering wheel buttons, and cruise control function at every steering wheel position.
Without the clock spring, there would be no electrical communication between the steering wheel and the vehicle's electronics. Since the steering wheel constantly rotates, a rigid cable cannot be used – the clock spring solves this problem with a coiled flat ribbon cable that winds and unwinds as you steer.
How does a clock spring work?
The clock spring consists of a spirally coiled flat ribbon cable inside a round housing. When you turn the steering wheel, the cable unwinds on one side and winds up on the other – this keeps the electrical connection intact at every steering wheel position without mechanical strain.
The principle is comparable to a tape measure that retracts into its case. The stationary part of the housing is attached to the steering column, while the rotating part moves with the steering wheel. The internal conductors are long enough to allow several complete steering wheel rotations (typically 3-4 rotations in each direction).
Clock spring center position
During installation, the clock spring must be positioned exactly in the center position. This means: the flat ribbon cable is located precisely in the middle of its winding range. If the center position is incorrect, the cable can tear at full steering lock. New clock springs are therefore delivered from the factory secured in the center position.
What signals does the clock spring transmit?
The clock spring transmits all electrical signals between the steering wheel and the vehicle's electronics: the airbag ignition signal, horn signal, steering wheel buttons for radio and cruise control, and on multifunctional steering wheels also telephone and voice control. The airbag connection is the most safety-critical function.
| Signal | Function | Safety-relevant |
|---|---|---|
| Airbag ignition signal | Triggering the driver's airbag in an accident | Yes – life-critical |
| Horn | Activation of the signal horn | Yes – road traffic regulations |
| Steering wheel buttons | Control of radio, telephone, onboard computer | No |
| Cruise control | Activate/deactivate speed control | No |
| Steering angle sensor | Detection of steering angle for ESP | Yes – driving stability |
In modern vehicles with multifunctional steering wheels, more and more signals run through the clock spring. This makes it a central component for both comfort and safety.
How do you recognize a defective clock spring?
The typical signs of a defective clock spring are a continuously illuminated airbag warning light, a non-functioning horn, and failed steering wheel buttons. Scraping or scratching noises often occur when steering. Since the driver's airbag no longer deploys, the defect is safety-critical.
- Airbag warning light illuminates continuously – the control unit detects the interruption
- Horn does not work – signal no longer gets through
- Steering wheel buttons non-functional – radio, cruise control, telephone do not respond
- Scraping or scratching noises – audible when turning the steering wheel
- Sporadic failures – functions fail only at certain steering angles
A gradual defect often first shows itself through sporadic failures: the horn works sometimes, sometimes not – depending on the steering wheel position. This indicates a partial cable break in the clock spring.
What happens if the clock spring tears?
When a clock spring tears, the electrical connection to the steering wheel is completely interrupted. The driver's airbag can no longer deploy in an emergency, the horn is non-functional, and all steering wheel buttons fail. The airbag control unit stores a fault code and activates the warning light.
The vehicle remains drivable, but is no longer roadworthy. During a TÜV inspection, the illuminated airbag warning light results in failure. A defective clock spring should therefore be replaced in a specialist workshop as soon as possible.
Does Airbag24 repair clock springs?
No, Airbag24 does not offer clock spring repair or clock spring sales. Our specialty is the repair of airbag control units and the sale of simulators for seat occupancy mats. However, if your airbag warning light is on, the problem is not always the clock spring – often a defective airbag control unit is the cause.
- Airbag control unit repair: We repair defective airbag control units for all common makes and models
- Seat occupancy mat simulators: Suitable simulators for seat occupancy detection in our shop
- Consultation: Are you unsure whether the control unit or the clock spring is defective? We'll help you with diagnosis
Frequently asked questions about the clock spring
Here you'll find answers to the most important questions about the clock spring in your car.
Is the clock spring installed in every car?
Yes. Every vehicle with a driver's airbag has a clock spring or comparable slip ring. It is the only component that provides a reliable electrical connection across the steering wheel's axis of rotation.
Can you continue driving with a defective clock spring?
Technically the vehicle is drivable, but the driver's airbag is disabled and the horn does not work. Both are significant safety defects. The defect should be remedied immediately.
What does it cost to replace a clock spring?
The cost consists of the replacement part and installation. Depending on the vehicle model, the replacement part costs between 25 and 325 euros, plus workshop labor of approximately 100 to 200 euros for removal and installation. Variants with integrated steering angle sensors are the most expensive.
Can I replace the clock spring myself?
This is strongly discouraged. The replacement involves the airbag system and is subject to explosives regulations. Only trained specialists are permitted to work on airbag components. Improper installation can lead to unintended airbag deployment.