SRS Operation

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 a frontal impact exceeding a certain set limit. The system consists of the SRS unit (including safing sensor and impact sensor), the cable reel and driver's airbag, and front passenger's airbag.

Fig. 20 SRS Operation:

The SRS unit senses and judges impact force, and if necessary, ignites the inflator charges, Fig. 20. If battery voltage is low or power becomes disconnected, a built-in back-up power circuit provides constant level voltage.

For the SRS to operate:
1. Impact and safing sensors activate, and send electric signals to microprocessor.
2. Microprocessor computes a signal and sends it to air bag inflator.
3. Electrical energy is supplied to air bag inflator by battery, or back-up power unit if battery voltage is too low.
4. Inflator charges ignite and air bags deploy.
5. It will take approximately 0.1 second from start of air bag deployment until air bag is completely deflated.

Self-diagnosis System
A self-diagnosis circuit is built into the SRS unit; when the ignition switch is turned ON (II), 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.

For better serviceability, the memory will store the cause of the malfunction, and the data link circuit passes on the information from the memory to the data link connector.