Air Bag Systems: Description and Operation

SRS System Description:

PURPOSE
The SRS is a safety device which, when used in conjunction with the seat belt, is designed to help protect the driver (and front passenger) in the event of a frontal impact where the vehicle is exceeding a specified speed.

The system is composed of left and right dash sensors, the SRS unit (includes cowl sensors), the cable reel, driver's airbag and front passenger's airbag (Si 4wS, Si VTEC: USA, SR 4WS,SR-V: Canada models).

SRS System Diagram:

OPERATION
As shown in the diagram below, the left and right dash sensors are connected in parallel. The parallel set of sensors is connected in series to each airbag inflator circuit 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 sensors are located inside the SRS unit.
For the SRS to operate:
1. One or both cowl sensors and one or both dash sensors must activate.
2. Electrical energy must be supplied to the airbag inflator by the battery, or by the back-up power circuit if the battery voltage is too low.
3. The inflator charge must ignite and deploy the airbag.

It takes about 0.1 second from the beginning of the airbag deployment until it is completely deflated (frontal collision against a fixed wall at a speed of 30 mph (50 km/h).


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 off after about six seconds if the system is operating normally. If the light does not come on, or does not go off after six seconds, or if it comes on while driving, it indicates an abnormality in the system. The system must be inspected and repaired as soon as possible.