Passive Restraints
The passive restraints are referred to as Supplemental Restraint System (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. In addition, each front seat occupant must have their Active Head Restraint (AHR) unit properly adjusted in order to obtain its maximum safety benefit.
The SRS electrical circuits are continuously monitored and controlled by a microcontroller and software contained within the Occupant Restraint Controller (ORC). An airbag indicator in the Instrument Panel Cluster (IPC) illuminates from four to six seconds as a bulb test each time the status of the ignition switch 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.
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 (also known as G forces) 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. On domestic market vehicles, the Occupant Classification System (OCS) monitors the passenger side front seat to determine whether or not the passenger side front seat is occupied and, if the seat is occupied, classifies the size of the occupant. The Occupant Classification Module (OCM) then provides an additional logic input that is used by the ORC to determine the appropriate force with which the Passenger AirBag (PAB) and seat belt tensioner should be deployed.
The front seat belt retractor tensioners, front seat belt anchor tensioners, the front seat belt adaptive load limiters and the Knee AirBags (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 Seat AirBags (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. 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 SABIC units, the SAB units and under certain conditions, will also actuate the front seat belt retractor and anchor tensioners.
During a frontal vehicle impact, the KAB units work in concert with properly fastened and adjusted seat belts to restrain both the driver and the front seat passenger in the proper position for an airbag deployment. The KAB units also absorb and distribute the crash energy from the driver and the front seat passenger to the structure of the instrument panel. The seat belt tensioners remove the slack from the front seat belts to provide greater assurance that the driver and front seat passenger are properly positioned and restrained for a front airbag deployment. The adaptive load limiters for the front seat belts allow the ORC to control the belt pressure applied to the chests of the front seat occupants based upon the impact sensor inputs.
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 and adaptive load limiter units, 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 appropriate SYSTEM 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 STANDARD PROCEDURE or REMOVAL or 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.