Restraint systems (SRS schematic): Description and operation

The SRS is an electronically controlled, single point sensing system. The system comprises an airbag Electronic Control Unit (ECU), a driver’s airbag module, a passenger’s airbag module (optional), two seat belt pretensioners and a warning lamp. Interconnecting wiring for the system is contained in yellow sleeving and integrated into the vehicle harnesses. A rotary coupler connects the vehicle harness to the driver’ airbag module. On vehicles with a passenger’s airbag module, a link lead connects the module to the vehicle harness. An ISO 9141 K line (bi-directional) serial communication link connects the airbag ECU to the vehicle’s diagnostic socket.

SRS schematic

The system is operational only while the ignition is on. With the ignition on, any frontal collision is detected by the airbag ECU. If the impact is above the preset severity, the ECU sends out simultaneous fire signals to the airbag modules and the seat belt pretensioners. The airbag modules then deploy protective airbags in front of the driver and front seat passenger, and the seat belt pretensioners retract to tighten the front seat belts. Collision detection to full deployment of the airbags and pretensioners takes approximately 45 milliseconds.

WARNING: All the SRS parts, including the wiring harness, link lead (where fitted) and rotary coupler, must be renewed after the airbags and pretensioners have deployed.

1. Ignition power supply
2. Instrument pack
3. Warning lamp
4. Airbag ECU
5. Rotary coupler
6. Driver’s airbag module
7. Passenger’s airbag module
8. Seat belt pretensioners
9. Diagnostic socket