Air Bag Systems: Description and Operation
Fig.1 Side Airbag Location - Typical:
RESTRAINTS
Side Impact Airbag System
Vehicles equipped with the Side Impact Airbag System utilize two airbags mounted to each front seat back frame. This system is designed to protect occupants in the event of a side impact collision.
The Side Impact Airbag Control Module (SIACM) controls the seat back mounted airbags. If the SIACM determines the impact is severe enough, the appropriate airbag will inflate, tearing open the front seat back trim cover protecting the passengers. Once a seat back mounted airbag has been deployed, the complete seat back assembly and all damaged parts must be replaced.
CLOCK SPRING
The clock spring is mounted to the steering column behind the steering wheel. The clock spring is used to maintain a continuous electrical circuit between the wiring harness and the:
- Driver's airbag
- Speed control switches
- Horn switch
- BCM - Remote Radio Switches (optional)
The clockspring consists of a flat, ribbon like, electrically conductive tape which winds and unwinds with the steering wheel rotation.
DRIVER AIRBAG
WARNING: NEVER DISASSEMBLE THE DRIVER AIRBAG. THE DRIVER AIRBAG HAS NO SERVICEABLE PARTS.
Driver Airbag Location:
The driver side airbag module protective trim cover is the most visible part of the driver side airbag system. The driver side airbag module is mounted directly to the steering wheel. Located under the airbag module trim cover are the horn switch, the folded airbag cushion, and the airbag cushion supporting components. The resistive membrane-type horn switch is secured beneath a plastic tray that is mounted to the back side of the driver airbag trim cover.
The driver side airbag module cannot be repaired, and must be replaced if deployed or in any way damaged. The driver side airbag module trim cover and the horn switch are not serviceable separately from the driver airbag module.
The driver side airbag module includes a stamped metal housing to which the cushion and an inflator unit are attached and sealed. The conventional pyrotechnic-type inflator assembly is mounted to studs on the back of the airbag module housing. The inflator seals the hole in the airbag cushion so it can discharge the gas it produces directly into the cushion when supplied with the proper electrical signal. Following an airbag deployment, the airbag cushion quickly deflates by venting this gas towards the instrument panel through the porous fabric material used on the steering wheel side of the airbag cushion.
The protective trim cover is fitted to the front of the airbag module and forms a decorative cover in the center of the steering wheel. The inside of the trim cover has locking blocks molded into it that engage a lip on the airbag module nylon housing. A stamped metal retainer is placed over the inflator mounting studs on the back of the airbag nylon housing. A stamped metal retainer is placed over the inflator mounting studs The trim cover will split at predetermined breakout lines, then fold back out of the way along with the horn switch and tray unit upon airbag deployment.
IMPACT SENSOR
The Airbag System is a supplemental safety device designed to help protect the driver and passenger from serious injury; caused by a frontal impact of the vehicle.
The Occupant Restraint Controller's (ORC) internal impact sensor provides verification of the direction and severity of an impact. The sensor is mounted within the ORC.
The Occupant Restraint Controller (ORC) uses data collected from it's internal accelerometers to discriminate the direction and severity of an impact. The ORC will activate power stages internal to the module in order to deploy the driver and passenger side airbags once a predetermined threshold has been exceeded. The ORC is calibrated for a particular vehicle family and uses an advanced software algorithm to discriminate the severity and direction of any vehicle event.
OCCUPANT RESTRAINT CONTROLLER
The Occupant Restraint Controller (ORC) contains the accelerometer and energy reserve capacitor. The ORC is mounted on the tunnel floor pan, forward of the center console.
The accelerometer is located inside the ORC. The accelerometer provides confirmation of a crash, discriminating severity. The ORC monitors the system to determine the system readiness. The ORC may store sufficient energy to deploy the airbags for only two minutes after the battery is disconnected. The ORC contains on-board diagnostics, and will illuminate the AIRBAG warning lamp on the cluster when a fault occurs. The warning equipment is tested for a few seconds every time the vehicle is started.
PASSENGER AIRBAG
WARNING: NEVER DISASSEMBLE THE PASSENGER AIRBAG, THE PASSENGER AIRBAG HAS NO SERVICEABLE PARTS.
Fig.7 Airbag Component Location:
The Passenger Airbag is located beneath the instrument panel and pad assembly. The airbag is mounted to a bracket (welded to the floor pan) with three screws.
The instrument panel top pad is the most visible part of the passenger airbag system. Located under the instrument panel top pad are the airbag door, the passenger airbag cushion and the airbag cushion supporting components.
The passenger airbag includes an extruded housing within which the cushion and inflator are mounted and sealed. Two stamped metal brackets, one on each end of the housing, enclose the cushion and inflator and also serve as the mounting brackets for the airbag.
Following a passenger airbag deployment, the passenger side airbag and the instrument panel must be replaced. The passenger side airbag cannot be repaired, and must be replaced if deployed or in any way damaged.
The passenger inflator assembly is within the airbag housing. The inflator seals the hole in the airbag cushion so it can discharge the gas it produces directly into the cushion when supplied with the proper electrical signal. Following an airbag deployment, the airbag cushion quickly deflates by venting this gas through the discrete vent holes used on each end panel of the airbag cushion.
The passenger airbag is secured with screws to the instrument panel beneath the instrument panel top pad and above the glove box opening. The instrument panel top pad above the glove box opening conceals the airbag door and a predetermined hinge line beneath its decorative cover. Upon airbag deployment, the top pad will bend at the hinge line and the door will fold back out of the way onto the top of the instrument panel.
Fig.1 Side Airbag Location - Typical:
Fig.14 Seat Airbag - Typical:
SEAT AIRBAG
The side impact airbag system Seat Airbags are located in the outboard side of the front seat backs. One in each front seat. The seat airbag inflator assembly is within the airbag housing. Each airbag is mounted to the seat back frame.
Only the Side Impact Airbag Control Module (SIACM) can deploy the side airbags. When supplied with the proper electrical signal the seat airbag inflator will produce a gas and discharge the bag directly between the occupant and the side of the vehicle, protecting the occupant. Upon deployment, the seat back trim cover will tear open and allow the side airbag to fully inflate and quickly deflate.
SIDE IMPACT AIRBAG CONTROL MODULE
Fig.20 SIACM Position/Orientation:
Vehicles equipped with side impact airbags use two Side Impact Airbag Control Modules (SIACM). One is located on each respective side body B-pillar.
Fig.21 Side Impact Airbag System Component Location:
Each Side Impact Airbag Control Module (SIACM) serves as the impact sensor for its seat mounted airbag. The right side SIACM controls the right seat airbag. The left side SIACM controls the left seat airbag. Each SIACM contains two accelerometers, both accelerometers must agree in order to deploy the side airbag. In the event of a side impact the appropriate SIACM will send a electronic signal to its airbag, deploying the airbag. The SIACM communicates with the occupant restraint controller via the PCI bus circuit.
AIRBAG SYSTEM/OCCUPANT RESTRAINT CONTROLLER SYSTEM
The Airbag System is equipped with a new type of Airbag Control Module (ACM) called an Occupant Restraint Controller (ORC). The ORC is secured to a bracket on the floor panel transmission tunnel below the instrument panel inside the vehicle. The ORC mounting bracket also serves as the instrument panel center support. The ORC contains a microprocessor, the impact sensor, and energy storage capacitors. The microprocessor contains the airbag system logic. The airbag system logic includes On-Board Diagnostics OBD capability, and communicates with the instrument cluster circuitry on the Programmable Communication Interface (PCI) data bus to control the airbag indicator lamp. The microprocessor in the ORC monitors the impact sensor signal and the airbag system electrical circuits to determine the system readiness. If the ORC detects a monitored system fault, it sends messages to the Mechanical Instrument Cluster (MIC) over the PCI data bus to turn ON the airbag warning lamp. A pre-programmed decision algorithm in the ORC microprocessor determines when the deceleration rate is severe enough to require airbag system protection. When the programmed conditions are met, the ORC sends an electrical signal to deploy the airbag system components. The impact sensor is an accelerometer that senses the rate of vehicle deceleration, which provides verification of the direction and severity of an impact. The impact sensor is calibrated for the specific vehicle, and is only serviced as a unit with the ORC. The ORC also contains an energy-storage capacitor. This capacitor stores enough electrical energy to deploy the airbags, for two minutes following a battery disconnect or failure during an impact. The purpose of the capacitor is to provide airbag system protection in severe secondary impact if the initial impact has damaged or disconnected the battery, but not severe enough to deploy the airbags. The ORC cannot be repaired or adjusted and, if damaged or faulty, it must be replaced
WARNING: THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENTS YOU MUST FIRST DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. WAIT TWO MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY. NEVER STRIKE OR KICK THE AIRBAG CONTROL MODULE, AS IT CAN DAMAGE THE IMPACT SENSOR OR AFFECT ITS CALIBRATION. IF AN OCCUPANT RESTRAINT CONTROLLER IS ACCIDENTALLY DROPPED DURING SERVICE, THE MODULE MUST BE SCRAPPED AND REPLACED WITH A NEW UNIT.
The airbag warning lamp is the only point at which the customer can observe "symptoms" of a system malfunction. Whenever the ignition key is turned to the "run" or "start" position, the MIC performs a lamp check by turning the AIRBAG warning lamp ON for 6-8 seconds. If the lamp remains off, it means that the ORC has checked the system and found it to be free of discernible malfunctions. If the lamp remains ON, there could be an active fault in the ORC system or the MIC lamp circuit may be internally shorted to ground.