SRS Operation: General

In a collision, the sudden deceleration or acceleration is measured by the safing sensor in the restraints control module (RCM) and by the impact sensors. The restraints control module (RCM) evaluates the readings to determine the impact point on the vehicle and whether the deceleration/acceleration readings exceed the limits for firing any of the air bags or pretensioners. During a collision, the restraints control module (RCM) only fires the air bags and pretensioners if the safing sensor confirms that the data from the remote sensor(s) indicates an impact limit has been exceeded. The restraints control module (RCM) also monitors the vehicle for a roll-over accident using the internal roll-over sensor and high speed controller area network (CAN) bus messages from the anti-lock brake system (ABS) module and the steering angle sensor.

The restraints control module (RCM) incorporates the following impact thresholds to cater for different accident scenarios:

• Front impact, pretensioners.
• Front impact, driver and passenger air bags stage 1, belt unfastened.
• Front impact, driver and passenger air bags stage 2, belt unfastened.
• Front impact, driver and passenger air bags stage 1, belt fastened.
• Front impact, driver and passenger air bags stage 2, belt fastened.
• Rear impact.
• LH (left-hand) side impact.
• RH (right-hand) side impact.
• Roll-over.

The front impact thresholds increase in severity from pretensioners, through to driver and passenger air bag stage 2, belt fastened.