Control Module

The primary task of the supplemental restraint system module (SRS) is to minimize injuries to the driver and passengers in the event of different types of accident. To do this, the control module validates incoming pulsed collision signals (acceleration signals generated by a collision) and then determines the required action.

The control module uses internal sensors as well as external collision sensors. Using the data collected from the sensors, the system determines which of the following will be activated:

• front airbags
• side impact protection (SIPS) bags
• inflatable curtains
• seat belt tensioners.

The collision sensor in the control module registers the longitudinal mechanical stress that occurs in a frontal collision. A side impact may also be registered in the collision sensor. The longitudinal stresses are measured using two acceleration sensors. If the longitudinal stresses exceed a certain level, the stress will be calculated (the collision pulse). The calculation evaluates whether the collision pulse was sufficient to activate the airbags and/or the seat belt tensioners. Airbags and seat belt tensioners can be activated individually.

The driver and passenger airbags and the seat belt tensioners are designed to deploy in the event of a frontal collision. There is an electrical switch in the control module to further increase the safety of the system. The switch must be activated in event of a collision for the front airbags to deploy.

When the collision protection system is activated, the control module transmits a pulsed current to the ignition mechanisms in the airbags and/or the seat belt tensioners. No seat belt tensioners or airbags will normally be activated in the event of a collision from the rear.

For the side impact cushion to deploy the collision required must be powerful enough that it is registered by the side impact sensor, as well as the SRS control module registering a collision. If the side impact occurs at the center of the car, the side impact protection (SIPS) bags and the inflatable curtain are deployed on the side where the collision occurred. If the side impact is towards the rear of the car, normally only the inflatable curtains on that side are deployed. For further information, see Deployment of side impact protection (SIPS) .

The control module has a collision recording function. This records certain system information in the event of up to three collisions. If necessary, this information can be analyzed and used after a collision. This information is used in the development of collision safety systems of the future.

There is an internal energy reserve in the control module. This is intended to run the whole system for a short time in the event of a voltage drop. This is to ensure the function of the system, if for example the battery cables should be cut or the battery loses power in some other way during a collision.

In the event of a collision a signal is sent from the SRS control module to the VGLA control module. The intention of the signal is to unlock the doors.

The SRS control module determines whether the airbags or seat belt tensioners should be deployed. This depends on whether:

• if the driver and front passenger are wearing seat belts or not
• if there is a fault in the seat belt buckles.

Information about use of the seat belt buckle for the driver and front passenger comes from the seat belt buckle sensors. If a fault occurs in either the driver or passenger seat belt buckles, a diagnostic trouble code (DTC) is stored locally in the SRS control module.

The SRS indicator lamp lights when the ignition is switched on. If no faults are registered by the control module, either internally or from the sensors, wiring or igniters, a signal is transmitted to the combined instrument panel confirming that the SRS indicator lamp can be switched off. If a fault occurs, the SRS control module transmits a signal to the combined instrument panel to light the SRS indicator lamp in the combined instrument panel.

Note that after a collision, it may be necessary to replace the wiring for the airbags and seat belt tensioners which deployed. This is because the connectors may melt at the moment of deployment. If a connector has melted, the wiring closest to it must be replaced.