Air Bag Systems: Description and Operation

SRS System Component Location:

PURPOSE
The SRS is a safety device which, when used in conjunction with the seat belt, is designed to protect the driver by operating only when the car receives a frontal impact exceeding a certain set limit. The system is composed of left and right dash sensors, the SRS unit (includes cowl sensor), the cable reel and airbag assembly.

SRS System Diagram:

OPERATION
As shown in the diagram below, the left and right dash sensors are connected in parallel. This parallel set of sensors is connected in series with the airbag inflator circuit, the cowl sensor, and the car battery. In addition, a back-up power circuit is connected in parallel with the car battery. The back-up power circuit and the cowl sensor are located inside the SRS unit.
For the SRS to operate:
1. Electrical energy must be supplied to the airbag inflator by the battery, or the back-up power circuit if the battery voltage is too low.
2. The cowl sensor and at least one dash sensor must be activated simultaneously for at least 0.015 seconds. The airbag will then deploy.


SELF-DIAGNOSIS SYSTEM
A self-diagnosis circuit is built into the SRS unit; when the ignition switch is turned ON, the SRS indicator light comes on and goes out after about 6 seconds if the system is operating normally. If the light does not come on, or does not go out after 6 seconds, or if it comes on while driving, this indicates an abnormality in the system. It must be inspected and repaired as soon as possible.