Control Module

The primary task of the supplemental restraint system module (SRS) is to minimize injuries to the driver and passengers in different types of accident. To do this, the control module measures the acceleration signals generated by a collision and then determines the required action. The control module has internal and external sensors. Using the data collected from the sensors, the control module determines which of the following protection systems will be activated:

• seat belt tensioners front seat
• front airbags
• adaptive steering column (USA/CDN only)
• adaptive seatbelt force limiter (USA/CDN only)
• seat belt tensioners rear seat
• side impact protection (SIPS) bags
• door mounted inflatable curtains
• ROPS (Roll Over Protection System).

The collision sensors in the control module and the frontal collision sensor and the side collision sensors register the mechanical stresses that occur in the event of a collision. The stresses are measured by the acceleration and pressure sensors. If the stresses exceed a certain level, the collision pulse starts to be calculated. The calculation evaluates whether the collision pulse was sufficient to activate the protection system. Airbags and seat belt tensioners can be activated individually.

Certain markets also use:

• an occupant weight sensor (OWS) located under the seat cushion on the front passenger seat
• two seat position sensors located on the rail under the driver's seat and front passenger seat.

The driver and passenger airbags and the seat belt tensioners are designed to deploy in the event of a frontal collision as necessary. In USA/CDN, the adaptive steering column and the function for adaptive seatbelt force limiting are also activated as necessary.

In the event of a side impact, the side airbags and the door mounted inflatable curtain on the impact side activate, as well as the seat belt tensioners in the front seat.

In the event of a rear impact, the front seat belt tensioners and the ROPS (Roll Over Protection System) are activated as necessary.

The control module has a local CAN network connected to it (only applies to USA/CDN). The occupant weight sensor (OWS) is connected to the controller area network (CAN). There is also a switch on the passenger side of the dashboard. This switch can be used to activate or deactivate the passenger airbag using the ignition key (does not apply to USA/CDN).

The control module also has an accident data recorder that records certain system information in the event of a collision. This information can be analyzed and used after a collision as necessary and is used to develop the supplemental restraint systems of the future. The control module can store information from 3 collisions. Once 3 collisions have occurred, no more information can be stored and the control module must be replaced. A diagnostic trouble code is generated when the control module has stored information from 3 collisions.

In the event of a frontal collision, side on collision, rear collision or a roll, a collision signal is transmitted from the supplemental restraint system module (SRS) to the phone module (PHM) and the central electronic module (CEM) using a directly connected cable. The purpose of this signal is to:

• switch off the fuel pump (FP)
• switch off the engine cooling fan (FC)
• switch off the windshield wipers when the car is stationary
• switch on the interior lighting and the courtesy lighting
• set the vehicle to collision status
• unlock the central locking system and
• if the vehicle is equipped with Volvo On Call (Plus), send an automatic alarm to CSC (Customer Service Center).

A collision signal is also sent to the phone module (PHM) and the central electronic module (CEM) via the Controller area network (CAN).

The supplemental restraint system module (SRS) decides to deploy the airbags and/or the seat belt tensioners and/or adaptive steering column and/or the function for adaptive seatbelt force limiting in the event of a frontal collision. 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
• if there is a fault in the controller area network (CAN) communication.

As a result of the above conditions, in the event of a low impact collision the seat belt tensioner may deploy on the driver's side (belted driver) while the airbag is deployed on the passenger side (non belted passenger).

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 via the CAN network to the Driver information module (DIM) confirming that the SRS indicator lamp can be switched off. If there is a fault, the supplemental restraint system module (SRS) transmits information to the driver information module (DIM) indicating which lamp should be lit and the text to be displayed in the combined instrument panel:

• The SRS warning lamp
• the general warning lamp or
• the yellow information light

The driver information module (DIM) continuously transmits information to the supplemental restraint system (SRS) control module via the controller area network (CAN) about the status of the SRS warning lamp.

If the SRS indicator lamp stops working, the general red warning lamp is used instead.

Note that after a collision, it may be necessary to replace the cable harness for the components of the protection system which have deployed. This is because the connectors may melt at the moment of deployment. If a connector has melted, the cable harness adjacent to the connector must be replaced.