Part 1
Design
Control module
WARNING: The battery must be disconnected before any work is carried out on the supplemental restraint system (SRS). Otherwise the airbags could accidentally deploy.
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 seat belt 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 seat belt 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).
NOTE: The on/off switch for the front passenger airbag and occupant weight sensor (OWS) must not be installed in the vehicle together.
The control module has a collision recording function. This records certain system information in the event of a collision. If necessary, this information can be analyzed and used after a collision. This information is used to develop the collision safety systems of the future. The control module can store information from 3 collisions. If 3 collisions have occurred no more information can be stored and the control module must be replaced. A diagnostic trouble code (DTC) is stored 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 seat belt 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) whilst 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 indicator 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 indicator 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.
WARNING: The battery must be disconnected before any work is carried out on the supplemental restraint system (SRS). Otherwise the airbags could accidentally deploy.
Side impact sensor
The side impact sensors in the vehicle are used to measure the mechanical stresses that occur in the event of a collision.
The four sensors which are used in the car are:
- 1 side impact sensor in each left and right B post
- 1 side impact sensor in each left and right door.
The side impact sensors in the B-post are acceleration sensors while the side impact sensors in the doors are pressure sensors. The sensors transmit data continuously to the control module. In the event of a collision, the control module uses the acceleration and pressure data from the sensors, and the control module's internal sensors to determine if the collision severity is enough to activate the side impact protection system.
Only the side impact protection system on the collision side is activated.
In the event of a fault in the side impact sensor, the control module stores a diagnostic trouble code (DTC). A diagnostic trouble code (DTC) is also stored if the communication between the control module and one of the side impact sensors does not function. Each side impact sensor has a serial number. The serial number is used to check that the correct side impact sensor is installed.
If one (or several) of the side impact sensors stops functioning, the control module uses the remaining sensor to determine when the collision protection should be activated.
NOTE: The side impact sensors in the B-posts are the same and can be installed on the left or right side, but cannot be used in the doors. The side impact sensors in the doors are also the same and can be either installed in the left or right door.
Data is transmitted on the same cable used for power supply. There is a signal/power supply cable to each side impact sensor and a ground lead.
Frontal impact sensor
The frontal impact sensors are used to provide the supplemental restraint system module (SRS) with advance information about the collision pulse. This enables the control module to determine the components to be activated more accurately.
The frontal impact sensors have integrated logic which transmits acceleration data to the supplemental restraint system module (SRS) in the same way as the side impact sensors.
In the event of a collision, the control module calculates the acceleration data from the frontal collision sensors and the internal sensors of the control module to check if the impact is sufficiently great to activate the frontal impact protection.
In the event of a fault in a frontal impact sensor, the control module stores a diagnostic trouble code (DTC). A diagnostic trouble code (DTC) is also stored if the communication between the control module and one of the frontal impact sensors does not function. Each frontal impact sensor has a serial number. The serial number is used to check that the correct frontal impact sensor is installed.
If one or both of the frontal impact sensors stops functioning, the control module uses the remaining acceleration sensor to determine when the collision protection should be activated.
Data is transmitted on the same cable used for power supply. There is a signal/power supply cable to each frontal impact sensor and a ground lead.
The two frontal impact sensors are behind the left and right-hand headlamps.
Seat position sensors (USA/CDN only)
The seat position sensor is used to determine the size of the person sitting on the seat. There are two seat position sensors in the vehicle, one under the driver's seat and one under the front passenger seat. The seat position sensors are directly connected to the supplemental restraint system module (SRS). The seat position sensors have separate signal cables to the control module and a common ground.
The seat position sensor consists of a Hall sensor which modifies the current depending on the position of the seat. The seat position sensor has two classifications, these are a small person and a large person. A small person means that the seat is approximately 10 cm from the first seat position and forwards. Other positions are classified as a large person.
This information is used by the function for adaptive seat belt force limiting.
Switch on/off, front passenger airbag (not USA/CDN)
This switch is used to activate or deactivate the front passenger airbag. The switch is on the side of the dashboard on the passenger side. The switch can only be accessed with the front passenger door open. The ignition key is used to change the position of the switch. When the switch is in the "OFF" position, all the stages of the passenger airbag are deactivated and the passenger airbag disconnected (PAD) warning lamp lights.
The position of the switch is determined by two Hall sensors. The Hall sensors for the switch are directly connected to the supplemental restraint system module (SRS). Each Hall sensor is individually connected to the control module. The signal which is transmitted from the Hall sensors has two different current levels, depending on the position of the switch.
A diagnostic trouble code (DTC) is stored if the signal from the Hall sensors cannot be correctly interpreted. The control module may, depending on the fault, deactivate the passenger airbag. The PAD (passenger airbag disconnected) warning lamp and the SRS indicator lamp light and a text message is displayed in the Driver information module (DIM) if the passenger airbag is deactivated. If a fault is detected and the passenger airbag is not deactivated, the SRS indicator lamp lights and a text message is displayed in the driver information module (DIM).
NOTE: The on/off switch for the front passenger airbag and occupant weight sensor (OWS) must not be installed in the vehicle together.
Occupant weight sensor (OWS) (USA/CDN only)
The occupant weight sensor (OWS) consists of three interactive components:
- The pressure sensor, installed under the front passenger seat
- The seat belt force sensor, mounted in the seat frame on the outside of the front passenger seat
- Occupant weight sensor module, installed under the front passenger seat.
The pressure sensor registers the pressure the seat is exposed to, for example when someone is sitting in the car. Information from the seat belt force sensor is also used to ensure the good performance of the system. The seat belt force sensor informs the occupant weight sensor module what force the belt is tensioned with. This is done because the pressure measured by the pressure sensor can be affected by the passenger fastening the seat belt over themselves or child seat tightly. This means that the passenger or child seat exerts greater pressure on the seat than during normal seat belt use. The passenger or child seat is then interpreted as being heavier than he or she is. The occupant weight sensor module uses the information from both the pressure sensor and seat belt force sensor to calculate the actual weight of the passenger. The occupant weight sensor (OWS) transmits continuous signals on the local controller area network (CAN) which the supplemental restraint system module (SRS) and occupant weight sensor (OWS) are connected to. If the occupant weight sensor (OWS) does not function correctly the supplemental restraint system module (SRS) will:
- deactivate the front passenger airbag
- light the warning lamp for passenger airbag disconnected (PAD) in the roof console
- light the SRS (supplemental restraint system) indicator lamp and display the alert message in the driver information module (DIM).
If a fault occurs in any of the components the following should be noted:
- The pressure sensor and occupant weight sensor module must be replaced at the same time
- The seat belt force sensor is replaced separately.
NOTE: The on/off switch for the front passenger airbag and occupant weight sensor (OWS) must not be installed in the vehicle together.
Adaptive seat belt force limiter (USA/CDN only)
WARNING:
- Never use an ohmmeter or similar tool to test airbags, door mounted inflatable curtains, adaptive seat belt tensioners, the adaptive steering column, rollover bar cassette or seat belt tensioners.
Disconnect airbags, door mounted inflatable curtains, adaptive seat belt tensioners, adaptive steering column, rollover bar cassette or seat belt tensioners before testing them. Failure to do so may result in accidental deployment. This could result in serious injury or death.
The adaptive seat belt force limiter improves the seat belt function in the event of a frontal collision when the airbag has been activated. There are two adaptive seat belt force limiters in the car. These are integrated in the seat belt reel, positioned at shoulder height on the driver's and front passenger seat belts.
The adaptive seat belt force limiters are electrically separated from each other. The adaptive seat belt force limiters have a pyrotechnic charge which adapts the seat belt force to a lower level against the chest on activation.
The adaptive seat belt force limiter, seat belt reel, seat belt (inertia) reel sensor and seat belt tensioner are installed in a single unit. In the event of a fault in any of these the whole unit must be replaced.
Adaptive steering column (USA/CDN only)
WARNING:
- Never use an ohmmeter or similar tool to test airbags, door mounted inflatable curtains, adaptive seat belt tensioners, the adaptive steering column, rollover bar cassette or seat belt tensioners.
Disconnect airbags, door mounted inflatable curtains, adaptive seat belt tensioners, adaptive steering column, rollover bar cassette or seat belt tensioners before testing them. Failure to do so may result in accidental deployment. This could result in serious injury or death.
When the collision protection system in the collapsible steering column is activated, a pin deploys enabling the steering column to be adjusted for length. The steering wheel is pressed in further towards the dashboard than if the steering column was rigid.
The steering is not affected by the deployment of the pin. The pin is deployed by a pyrotechnical charge and is located in the center of the steering column. The collision protection system in the adaptive steering column only activates if the driver is wearing the seat belt and if the airbag deploys. The entire steering column must be replaced if the collision protection system in the adaptive steering column has deployed.
Front airbags
WARNING: Never use an ohmmeter or similar tool to test airbags, door mounted inflatable curtains, adaptive seat belt tensioners, the adaptive steering column, rollover bar cassette or seat belt tensioners.
Disconnect airbags, door mounted inflatable curtains, adaptive seat belt tensioners, adaptive steering column, rollover bar cassette or seat belt tensioners before testing them. Failure to do so may result in accidental deployment. This could result in serious injury or death.
The airbags at the front of the vehicle are:
- driver airbag, 2 stage deployment
- front passenger airbag, 2 stage deployment.
The driver's airbag is located in the steering wheel. The passenger airbag is located above the glove compartment in the dashboard.
The front airbags have two ignition components each. These are electrically separated from each other. This means that the different ignition components have their own separate power supply and grounding points from the control module. Two power supply outputs are required from the control module for each airbag, one for each ignition component. This means that in total four pins on the control module, two power supply pins and two ground pins, are used for each airbag.
When activating the airbags electrical signals are transmitted from the supplemental restraint system module (SRS) to the relevant airbag stage.
Stage 1
Stage 1 of the driver's airbag is pyrotechnic. In the event of activation the charge combusts and the gas which develops is blown into the airbag.
Stage 1 on the passenger airbag consists of a pyrotechnic component in combination with a reservoir which stores a gas. On activation the pyrotechnic charge combusts and mixes with the stored gas. The gas mixture inflates the airbag.
Stage 2
Stage 2 of the driver's and passenger airbags is pyrotechnical. In the event of activation the charge combusts and the gas which develops inflates the airbag.
The pace of the airbag 2 stage activation is dependent on the collision type and seat belt use. Both stages always activate. The difference is that in the event of a lesser impact, there is a greater time delay between stage 1 and stage 2. For more serious impacts the time delay is shorter between stages 1 and 2, which gives a stiffer airbag.
WARNING: Never use an ohmmeter or similar tool to test airbags, door mounted inflatable curtains, adaptive seat belt tensioners, the adaptive steering column, rollover bar cassette or seat belt tensioners.
Disconnect airbags, door mounted inflatable curtains, adaptive seat belt tensioners, adaptive steering column, rollover bar cassette or seat belt tensioners before testing them. Failure to do so may result in accidental deployment. This could result in serious injury or death.
Side impact air bags
WARNING: Never use an ohmmeter or similar tool to test airbags, door mounted inflatable curtains, adaptive seat belt tensioners, the adaptive, steering column, rollover bar cassette or seat belt tensioners.
Disconnect airbags, door mounted inflatable curtains, adaptive seat belt tensioners, adaptive steering column, rollover bar cassette or seat belt tensioners before testing them. Failure to do so may result in accidental deployment. This could result in serious injury or death.
There are two side impact protection (SIPS) bags connected to the supplemental restraint system module (SRS). Their connectors are electrically separated from each other. The side impact protection (SIPS) bags are on the outside of the backrest, underneath the upholstery, on the front seats. The side impact protection (SIPS) bags deploy on the side of the impact. Their task is to protect the hips, chest and upper body in the event of a side on collision. The side airbags together with the door mounted inflatable curtains and other safety systems can help to protect the driver and front passenger in the event of a collision.
The side impact protection (SIPS) bag uses a pyrotechnic component in combination with a reservoir which stores a gas. On activation the pyrotechnic charge combusts and mixes with the stored gas. The gas mixture inflates the airbag.
WARNING: Never use an ohmmeter or similar tool to test airbags, door mounted inflatable curtains, adaptive seat belt tensioners, the adaptive steering column, rollover bar cassette or seat belt tensioners.
Disconnect airbags, door mounted inflatable curtains, adaptive seat belt tensioners, adaptive steering column, rollover bar cassette or seat belt tensioners before testing them. Failure to do so may result in accidental deployment. This could result in serious injury or death.