Air Bag Systems: Description and Operation
Fig. 1 Airbag Restraint System:
PURPOSE
- The Supplemental Restraint System (SRS) is designed to supplement the driver and passenger seat belts to help reduce the risk or severity of injury to the front seat occupants by activating and deploying a driver and passenger (if equipped) side air bag in certain frontal collisions.
- The system is most effective when used in conjunction with the seat belt system, but it will operate and provide a reduced measure of protection even without seat belts being used.
OPERATION
Air Bag Warning Lamp
Whenever the ignition key is turned to the RUN or START position, the Air Bag warning lamp on the instrument cluster lights and stays lit for 6 to 8 seconds.
- This means that the Airbag Diagnostic Module or Passenger Airbag Diagnostic Module (ASDM or PASDM) has checked the system and found it to be free of discernible malfunctions.
- The "Air Bag" warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer.
Self Diagnosis
The ASDM (PASDM) monitors critical input and output circuits within the air bag system, making sure they are operating correctly.
- The ASDM (or PASDM) contains a safing sensor, an integral sensor in the circuitry of the system that is used to deploy the air bags.
- Some circuits are tested continuously; others are checked only under certain circumstances.
- The ASDM (or PASDM) provides diagnostic information about the air bag system through the DRBII.
Deployment
- The deceleration resulting from the impact of a front-end collision causes the switch inside of the ASDM (or PASDM), safing sensor to be closed.
- As soon as one front sensor and the safing sensor are closed, an electrical charge is sent to the air bag module.
- This actuates the inflator, which produces a quantity of nitrogen gas, deploying the air bag.
- The total time from the closure of the switches to deployment and deflation of the air bag is 1/10th of a second.
Warning: The fasteners, screws and bolts used for airbag components have special coatings and are specifically designed for the airbag system. They must not be replaced with substitutes. If fastener replacement is required, use the correct fasteners provided in the service package.
Components
The major components of the SRS are;
- The Airbag Module
- The Clockspring
- The Impact Sensors
- The Airbag System Diagnostic Module (ASDM or PASDM).
If any of these parts should fail, they must be replaced, as they cannot be repaired.
Note: Use the test procedures in Testing & Inspection to find the cause of any customer complaint regarding the "Air Bag" warning lamp.
Glossary Of Terms Used
Active Codes: A malfunction that is present now.
ACM: Airbag Control Module (also called the Air Bag System Diagnostic Module (ASDM)).
ASDM: Air Bag System Diagnostic Module (also called the Airbag Control Module (ACM)).
Air Bag Module: Also called "Squib" initiator - located inside the air bag module assembly.
Impact Sensor: G force sensitive, threshold switches which close when an impact of sufficient force in the correct direction occurs.
An impact switch closure accompanied by closure of the safing sensor, alerts the control module that it is now time to deploy the airbag(s).
Initiator: Also called "Squib" - located inside the air bag module assembly.
PASDM: Passenger Air Bag System Diagnostic Module
Safing Sensor: A switch inside the ASDM which must be closed at the same time at least one of the impact sensors is closed, to initiate deployment of the airbag(s).
Squib: Also called "Air Bag Module" initiator - located inside the air bag module assembly.
SRS: Supplemental Restraint System
Stored Codes: A malfunction that had been present during a previous key cycle, may or may not be active.