Control Module

The primary role of the supplemental restraint system module (SRS) is to reduce the degree of injury to the driver and passengers in various types of accidents. It does so by measuring incoming impact pulse signals (acceleration signals that arise during a collision) and then select suitable action.

The control module is aided in its task by internal and external impact sensors. Based on sensor data, the system determines whether any of the following should be deployed:

• front airbags
• side impact protection (SIPS) bags
• inflatable curtains
• seat belt tensioners
• adaptive steering column
• adaptive seatbelt force limiter (USA/CDN only).

The impact sensor in the control module registers the mechanical stresses that arise from a head-on collision. The impact sensor can also register a collision from the side. The stresses are measured via an acceleration sensor. Two front impact sensors are used to register any stresses from a head-on impact. When the stresses exceed a certain level, a calculation of the stress (impact pulse) is initiated. The calculation determines whether the impact pulse is significant to deploy the airbags and/or belt tensioners. Airbags and belt tensioners can be deployed 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
• two belt retractor sensors located at shoulder height in the front belt retractors.

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-on collision, the side impacts sensors are used to register stresses. If the side impact is toward the front of the vehicle, the side airbag and inflatable curtain are deployed on the side of the vehicle the collision occurred. If the side impact is toward the rear of the vehicle, the inflatable curtain alone is deployed on the side of the vehicle the collision occurred.

No seat belt tensioners or airbags will be activated in the event of a collision from the rear.

The control module is connected to a local CAN network (USA/CDN only). The occupant weight sensor (OWS) is connected to the local CAN network.

There is also a switch on the end of the dashboard (on the passenger side) to enable or disable the front passenger airbag using the ignition key (not 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 or rear collision 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 windshield wipers when the car is stationary
• light the interior lighting
• light warning lamps
• unlock the doors and
• send an automatic alarm to CSC (Customer Service Center) when an accident has occurred - provided the vehicle is equipped with Volvo On Call (Plus).

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 belt tensioners in the event of a frontal collision.

This decision is based on factors such as:

• 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 situations described above, in the event of a low impact collision the seat belt tensioner may deploy on the driver's side while the airbag is deployed on the passenger side.

The SRS warning 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 warning 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 text should displayed in the combined instrument panel and which of the following lamps should be lit:

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

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 of the airbag or belt tensioner that has been deployed as the connector may melt at the moment of ignition. If a connector has melted, the cable harness closest to the connector must be replaced.