How to test an airbag clock spring (clockspring) |
​Airbag light going on

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Symptoms of a defective clockspring in a steering column switch

  1. Airbag warning signal light goes suddenly on when driving
  2. ​Airbag warning signal remains on all the time
  3. Beep alarm goes on immediately upon starting the engine
  4. Difficulty in using the horn, necessity to press several times on the steering wheel buttons
WARNING: NEVER TEST THE AIRBAG ITSELF OR TRY TO MEASURE ITS RESISTANCE WITH AN OHMMETER. RISK OF TRIGGERING THE PYROTECHNIC DEVICE AND DEPLOYING THE AIRBAG ! 

What is a clock spring (coil spring wire) and how does it work

The clock spring (steering column switch, contacts, contactor, etc.) allows the driver's airbag to be connected to the central airbag and safety belts pretensioning system. 
It also connects other commands and controls on the steering wheel like the horn buttons to the related ECU.
It is located immediately behind the steering wheel and is part of a single assembly that includes all controls behind the steering wheel referred to as steering column stalk or switch or controls, etc.
The most common driver's airbag defect by far is when the clock spring wire (flat flexible cable) gets damaged due to the repeated movements when steering. This occurs at a relatively high mileage like for example 150,000 km or more.
The airbag and horn cable is a flat flexible cable with as many pins as needed for the steering wheel controls and is shaped like a coil spring rolled up around the steering column.
It maintains the electrical contact with the steering column stalk PCB when steering and is therefore moving all the time, reducing its diameter when turning right and increasing it when turning left, helped by rubber ring springs as shown further below in this pictorial.
The coil cable is lubricated with grease to reduce and silence the friction of the wires and the grease becomes itself sticky with time which could result in the clock spring cable folding at one or more points and getting damaged.

Testing the steering coil spring wires to make sure of the airbag defect

You can either remove the whole steering column stalk assembly or simply take out the coil spring switch as shown in the below pictures.
The vehicle in this case is a Peugeot 208 fitted with a Valeo stalk assembly.
The clock spring can be separated from the rest of the steering column switch.
This shows the electronic board (PCB) that allows all controls behind the steering wheel to connect to the concerned control unit.
The disassembly of the clock spring shows the following:
  • A plastic body with a built-in beeper
  • The necessary rings to hold the coil in place
  • The flat cable with its connectors on both sides
  • The three rubber rings that act as springs to open the coil when steering left
The coil flat cable is shown here in the left picture.
For this Peugeot 208, it includes 6 pins and connectors as follows:
  • 2 pins used for the airbag 
  • 4 pins used for the horn buttons and other steering wheel controls, when available.

The picture to the right shows how the flat airbag cable folded in at least two places which should not occur as this ends up damaging the fragile thin conductors upon repeated steering and consequent cable folds and unfolds.
A test of the cable with an ohmmeter will determine and confirm the diagnostic of the coil spring wire.
Use an ohmmeter to measure the resistance pin to pin between both sides of the cable.
Try to move the cable while measuring (fold-unfold) to see if this impacts the reading.
The below measurements do show that:
  • the normal reading is 1.2 Ohms.
  • the pins #2 and #5 return a defective reading that changes when reshaping the flat cable
  • the readings are conforming to the symptoms which are a permanently lit airbag warning signal and a difficulty to use the horn
Pin
1
2
3
4
5
6
Ohm reading
1.2
5.5 to 25
1.2
1.2
5.5 to 34
1.2
Use
Airbag
Airbag
Horn
Horn
Horn
Horn
Test Result
OK
Defect
OK
OK
Defect
OK
The solution consists of ordering a new column steering stalk assembly using the part number shown on the label.
You have to make sure that you're ordering the exact part number that is compatible with your vehicle options.

Fitting a new steering clockspring

Click on the below button for the clock spring replacement:

See also our comprehensive tutorials for car maintenance: