Passive Restraints: Notes
The passive restraints are referred to as a 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 status of the ignition transitions to ON or Start. 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.
Vehicles manufactured for EMEA markets are equipped with a feature that allows PAB operation to be suppressed or enabled using a setup routine in the IPC. A passenger airbag ON/OFF indicator is located in the instrument panel switch pod in the instrument panel center stack. This indicator receives battery current whenever the status of the ignition is ON or START and illuminates only when the ORC pulls the appropriate indicator control circuit to ground. The indicator illuminates for about five seconds as a bulb test each time the status of the ignition transitions to ON or Start. Following the bulb test, the indicator is turned ON or OFF by the ORC based upon the electronic passenger airbag disable messages received from the IPC.
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, the rear outboard seat belt retractor tensioners (EMEA only) and the driver KAB (if equipped) are provided with a deployment signal by the ORC in conjunction with the front airbags. The side curtain airbags are provided with a deployment signal individually by the ORC based upon a side impact sensor input for the same side of the vehicle.
The ORC also contains a rollover sensor. Should the vehicle roll over and not cause any impact sensor to signal the need for a deployment, the rollover sensor in the ORC will deploy the side curtain airbags units, the SAB units and under certain conditions, will also actuate the front seat belt retractor and anchor buckle tensioners as well as the rear outboard seat belt retractor tensioners (EMEA only).
During a frontal vehicle impact, the static knee blockers work in concert with properly fastened and adjusted seat belts to restrain the front seat occupants in the proper position for an airbag deployment. The static knee blockers also absorb and distribute the crash energy from the front seat occupants to the structure of the instrument panel. 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 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 kilometer-per-hour (30 mile-per-hour) 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 DTC in its memory circuit and sends an electronic message to the IPC to turn ON the airbag indicator. The hard wired 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, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin out information and location views for the various wire harness connectors, splices and grounds.
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 SRS Load Tool special tool along with the appropriate Load Tool Jumpers and Adapters. Refer to the appropriate diagnostic information.