Passive Restraints: Operation
The passive restraints are referred to as SRS components because they were designed and are intended to enhance the protection for the occupants of the vehicle only when used in conjunction with the seat belts. They are referred to as passive restraints because the vehicle occupants are not required to do anything to make them operate; however, the vehicle occupants must be wearing their seat belts in order to obtain the maximum safety benefit from the factory-installed SRS components.
The SRS electrical circuits are continuously monitored and controlled by a microcontroller and software contained within the ORC. An airbag indicator in the IPC illuminates from four to six seconds as a bulb test each time the ignition switch is turned to the ON or START positions. Following the bulb test, the airbag indicator is turned ON or OFF by the ORC to indicate the status of the SRS. If the airbag indicator comes ON at any time other than during the bulb test, it indicates that there is a problem in the SRS electrical circuits. Such a problem may cause airbags not to deploy when required, or to deploy when not required.
Deployment of the SRS components depends upon the angle and severity of an impact. Deployment is not based upon vehicle speed; rather, deployment is based upon the rate of deceleration as measured by the forces of gravity (G force) upon the acceleration-type impact sensors, or by a pressure wave within a door as measured by the pressure-type impact sensor. When an impact is severe enough, the microcontroller within the ORC signals the inflator of the appropriate airbag units to deploy their airbag cushions.
The front seat belt retractor tensioners, front seat belt anchor tensioners, front seat belt adaptive load limiters and the KAB are provided with a deployment signal by the ORC in conjunction with the front airbags. The side curtain airbags (also known as the Side AirBag Inflatable Curtains/SABIC) and the SAB are provided with a deployment signal individually by the ORC based upon a side impact sensor input for the same side of the vehicle.
During a frontal vehicle impact, the seat belt tensioners remove the slack from the front seat belts to provide further assurance that the driver and front seat passenger are properly positioned and restrained for an airbag deployment. The adaptive load limiter and mechanical load limiter integral to each seat belt retractor controls the belt pressure applied to the chest of the wearer of that seat belt.
Typically, the vehicle occupants recall more about the events preceding and following a collision than they do of an airbag deployment itself. This is because the airbag deployment and deflation occur very rapidly. In a typical 48 km/h (30 mph) barrier impact, from the moment of impact until the airbags are fully inflated takes about 40 milliseconds. Within one to two seconds from the moment of impact, the airbags are almost entirely deflated. The times cited for these events are approximations, which apply only to a barrier impact at the given speed. Actual times will vary somewhat, depending upon the vehicle speed, impact angle, severity of the impact, and the type of collision.
When the ORC monitors a problem in any of the SRS circuits or components, including the seat belt tensioners, it stores a fault code or Diagnostic Trouble Code (DTC) in its memory circuit and sends an electronic message to the IPC to turn ON the airbag indicator. The hardwired circuits between components related to the SRS may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds. For proper wire repair, and connector repair procedures. Refer to CIRCUIT LOAD TESTING PROCEDURES , CONNECTOR TERMINAL REMOVAL and CONNECTOR TERMINAL INSTALLATION .
However, conventional diagnostic methods will not prove conclusive in the diagnosis of the SRS or the electronic controls and communication between other modules and devices that provide features of the SRS. The most reliable, efficient and accurate means to diagnose the SRS or the electronic controls and communication related to SRS operation, as well as the retrieval or erasure of a DTC requires the use of a diagnostic scan tool and may also require the use of the Airbag Kit. Refer to the appropriate diagnostic information.