SRS system description

SRS is an acronym for SUPPLEMENTARY restraint system. It is designed for use with a seatbelt, and with a seat belt, the chance of injury from the bag is negligible. Failure to wear a seat belt in an airbag equipped vehicle could result in serious injury or death.

Components

Airbag : Located on steering wheel
Slip ring : Wiring contact located on rear of steering wheel, designed to maintain electrical contact while still allowing wheel to turn
Crash sensors : One located on each inner fender above the wheel. These sensors detect deceleration forces and signal the control unit accordingly
Control unit : Located above the drivers right knee, the control unit determines via inputs, when to deploy the bag. It also monitors the system continuously and sets the fault warning lamp if a problem is detected.
Fault lamp : Located in the overhead check panel, the light tests for approximately 5 seconds after car is started, but will then go out unless faults exist in the SRS system. It includes a third crash sensor to confirm reports of deceleration from the front sensors.
Knee bolster : A padded steel guard behind the lower left dash trim panel. It's purpose is to prevent the driver sliding down into the wheel well during an accident, in such circumstances, the airbag could cause serious injury.

Items listed in green print must be replaced after deployment of airbag.

Description

The crash sensors monitor deceleration of the car. If that deceleration equates to a head on collision of at least 18km/h (11 mph) against an immovable object, the signal will be sent back to the control unit.

The control unit also contains a crash sensor, and if it determines that an accident is occurring, signals the airbag to fire. The airbag is fired by an igniter that fires a gas generator. This burns a solid fuel mixture which fills the bag with a non poisonous gas in less than 30 milliseconds. The gas then escapes through two holes in the rear of the bag and the bag deflates almost instantly.

The system is continuously monitored by the control unit, if a fault is detected the lamp will either come on continuously, or flash for approximately 5 minutes before illuminating continuously.

If faults are suspected, check flash codes before disconnecting battery to work on the system. Loss of battery power will clear any stored faults

E30 M3 Repair Manual V2.7. Copyright Š1999-2001 Koala Motorsport & Brett Anderson