Air Bag Systems: Description and Operation
CLOCKSPRINGThe clockspring assembly is mounted near the top of the steering column behind the steering wheel. The clockspring is used to maintain a continuous electrical circuit between the fixed instrument panel wire harness connector on the steering column and several electrical components that rotate with the steering wheel. The rotating components include the driver airbag, the horn switch, and the vehicle speed control switches.
The clockspring cannot be repaired. If the clockspring is faulty, damaged, or if the driver airbag has been deployed, the clockspring must be replaced.
The clockspring assembly consists of a plastic case which contains a flat, ribbon-like, electrically conductive tape that winds and unwinds like a clockspring with the steering wheel rotation. The electrically conductive tape consists of several fine gauge copper wire leads sandwiched between two narrow strips of plastic film.
Like the clockspring in a timepiece, the clockspring tape has travel limits and can be damaged by being wound too tightly. To prevent this from occurring, the clockspring is centered when it is installed on the steering column. Centering the clockspring indexes the clockspring tape to other steering components so that it can operate within its designed travel limits. However, if the clockspring is removed for service or if the steering column is disconnected from the steering gear allowing the clockspring tape to change position relative to the other steering components, it must be re-centered following completion of the service or it may be damaged. Refer to Restraints, Clockspring, Standard Procedure - Clockspring Centering.
Service and Repair
CURTAIN AIRBAG
Vehicles equipped with the Side Impact Airbag System utilize two Curtain Airbags mounted in each respective side of the headliner, stretching from the middle of the A-pillar at the instrument panel along the roof line to the C-pillar at the rear shelf panel. This system is designed to provide supplemental restraint to driver or outboard passengers in the event of a side impact collision.
The Side Impact Airbag Control Module (SIACM) controls the curtain airbags. If the SIACM determines the impact is severe enough, the appropriate SIACM will send a message to inflate the respective curtain airbag. The appropriate airbag will inflate, dropping down from the ceiling between the headliner and windows/pillars, to provide supplemental restraint to driver or outboard passengers in the event of a side impact collision. Once a curtain airbag has been deployed, the complete curtain airbag, headliner, upper A, B, and C-pillar trim panel, and all damaged parts must be replaced on the deployed side.
DRIVER AIRBAG
WARNING: THE DRIVER AIRBAG TRIM COVER AND HORN SWITCH ASSEMBLY ARE THE ONLY SERVICEABLE PARTS OF THE DRIVER AIRBAG. DO NOT DISASSEMBLE OTHER PARTS WITHIN AS THEY ARE NOT SERVICEABLE.
The Driver Airbag located in the center of the steering wheel is the most visible part of the system. It contains the airbag inflator, cushion, cover assembly, and their supporting components. The airbag utilizes a dual stage inflator and two initiator wire connections. the trim cover assembly, consisting of cover and horn switch in the only serviceable part of the airbag. The cushion, inflator, and inflator adaptor are covered with a wrap so the cushion does not unfold when servicing the trim cover and horn switch assembly
When supplied with the proper electrical signal from the ORC, the inflator produces gas and discharges it directly into the pillow. The airbag will deploy and the pillow will fully inflate.
OCCUPANT RESTRAINT CONTROLLER
The Occupant Restraint Controller (ORC) contains the impact sensor and energy reserve capacitor. The sensor is calibrated for the specific vehicle and reacts to the severity and direction of the impact.
The ORC monitors the system to determine the system readiness. The ORC stores sufficient energy to deploy the airbags in case battery power is lost prior to impact. The ORC contains on-board diagnostics, and illuminates the AIRBAG warning lamp in the cluster when a diagnostic trouble code occurs. The warning equipment is tested for a few seconds every time the vehicle is started.
PASSENGER AIRBAG
WARNING: NEVER DISASSEMBLE THE PASSENGER AIRBAG, THERE ARE NO SERVICEABLE PARTS WITHIN.
The most visible part of the Passenger Airbag is the passenger airbag decorative cover located just above the front right side of the instrument panel.
The passenger airbag is mounted to the instrument panel assembly. The passenger inflator assembly is within the airbag housing. The airbag is mounted to the instrument panel retainer and support structure.
The Passenger Airbag consists of:
- Dual Initiator Inflator Assembly
- Reaction Canister
- Airbag Pillow
- Passenger Airbag Cover/Door
When supplied with the proper electrical signal from the ORC, the inflator produces gas and discharges it directly into the pillow. The airbag will deploy and the pillow will fully inflate.
SEAT BELT & RETRACTOR - FRONT OUTBOARD
The seat belt system incorporates Tensioner Modules. They are integral to the front seat belt retractors and cannot be serviced. If found defective they must be replaced. In the event of an impact, the retractor assembly must be replaced regardless of belt condition. The tensioner is a one time pyrotechnic device.
At the onset of an impact event, each tensioner uses a pyrotechnic device which is triggered simultaneously with the front airbags to rapidly retract the seat belts. With the slack removed, the occupant's forward motion in an impact will be reduced as will the likelihood of contacting interior components. After an impact that deploys the airbags, the seat belt tensioner assembly must be replaced.
The Occupant Restraint Controller (ORC) monitors the seat belt tensioner circuit resistance and reports active and stored Diagnostic Trouble Codes (DTC's) if any problem is found.
WARNING: WHEN THE FRONT AIRBAG IS DEPLOYED, THE TENSIONER WILL HAVE DEPLOYED ALSO AND MUST BE REPLACED.
SEAT BELT TENSIONER - JR27 ONLY
The seat belt system incorporates Seat Belt Tensioners. The tensioner is designed to hold the occupant in their respective seat by retracting the seat belt up to four inches. They are integral to the front seat belt buckles and cannot be serviced. If found defective they must be replaced. After an airbag deployment, the tensioner must be replaced.
At the onset of an impact event, each tensioner uses a pyrotechnic device which is triggered simultaneously with the airbags to rapidly retract the seat belts. With the slack removed, the occupant's forward motion in an impact will be reduced as will the likelihood of contacting interior components. After an impact that deploys the airbags, the seat belt tensioner assembly must be replaced.
The Occupant Restraint Controller (ORC) monitors the seat belt tensioner circuit resistance and reports active and stored Diagnostic Trouble Codes (DTC's) if any problem is found.
Once a vehicle has been in an accident, the tensioner must be replaced along with any deployed air-bags and broken or damaged parts. Refer to the proper Body Diagnostic Procedures manual for diagnosis and testing.
WARNING: WHEN THE FRONT AIRBAG IS DEPLOYED, THE TENSIONER WILL HAVE DEPLOYED ALSO AND SHOULD BE REPLACED.
SIDE IMPACT AIRBAG CONTROL MODULE
Vehicles equipped with side impact airbags use two Side Impact Airbag Control Modules (SIACM). One is located on each respective side body B-pillar.
The impact sensor provides verification of the direction and severity of the side impact. The right side SIACM controls the right seat airbag. The left side SIACM controls the left seat airbag. In the event of a side impact the appropriate SIACM will send an electronic signal to its airbag, deploying the airbag. The SIACM communicates with the Occupant Restraint Controller (ORC) via the PCI bus circuit.
The accelerometer pulses are sent to a microprocessor, which contains a decision algorithm. When an impact is severe enough to require airbag protection, the SIACM microprocessor sends a signal to deploy the side airbag that completes the electrical circuits to the right or left side airbag. The sensor is calibrated for the specific vehicle and reacts to the severity and direction of the impact.
Each SIACM has its own energy reserve capacitor. This is to insure that the airbag may be fired even if the battery power is lost at time of impact.