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 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).
Note! The activating switch, on/off, for the front passenger airbag and occupant weight sensor (OWS) must not be installed in the vehicle together.
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.
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
S40/V50
C30
The vehicle's side impact sensors are used to provide the supplemental restraint system (SRS) early information on a side-on collision.
The four sensors that are used in the S40/V50 are:
- 1 side impact sensor in each left and right B post
- 1 side impact sensor in each left and right C post.
The four sensors that are used in the C30 are:
- 1 side impact sensor in each left and right B post
- 1 side impact sensor (pressure sensor) in each left and right door.
The side impact sensors in the B and C posts consist of acceleration sensors that continuously send data to the control module.
The side impact sensors (pressure sensors) in the doors (only C30) consist of air pressure sensors that continuously send data to the control module.
In the event of a collision, the control module uses the data from the sensors to determine if the collision force is sufficient to activate the side impact protection.
Only the side impact protection system nearest the point of impact is deployed.
In the event of a fault in the side impact sensor, a fault signal is transmitted to the control module which then 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.
If one (or both) of the side impact sensors stops working for some reason, the control module uses information from the other sensors to determine when to deploy the impact protection.
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 cable.
The side impact sensors in the B and C posts are of the same type and can be installed in all positions.
The side impact sensors (pressure sensors) in the doors (only C30) are of the same type and can be installed in either the left or right-hand door.
Each side impact has a serial number that is used to check that the right side impact sensor is installed in the vehicle.
Front impact sensor
The front 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 more accurately the components to be activated.
The front 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 front impact sensors and the internal sensors of the control module to check if the damage is sufficiently great to deploy the front impact protection.
In the event of a front impact sensor fault, a fault signal is sent to the control module, which generates a diagnostic trouble code. A trouble code is also generated if there is faulty communication between the control module and any of the front impact sensors. Each front impact sensor has a serial number that is used to check that the right front impact sensor is installed.
If one or both of the front impact sensors stops functioning, the control module uses the internal acceleration sensor to determine when the impact protection should be deployed.
Data is transmitted on the same cable used for power supply. There is a signal/power supply cable to each front impact sensor and a ground cable.
The two front impact sensors are behind the left and right-hand headlamps.
Belt retractor sensor (USA/CDN only)
The belt retractor sensor monitors the status of belt extension.
The belt retractor sensor sends information on the status of belt extension to the control module in real time. The control module then analyzes the obtained values and uses the results so that the belt force limiter can optimize belt force for the person occupying the seat.
There are two belt retractor sensors in the vehicle - one on the driver's side belt retractor and one on the front passenger side belt retractor.
Data is transmitted on the same cable used for power supply. There is a signal/power supply cable for each belt retractor sensor as well as a ground cable.
The adaptive belt force limiter, belt retractor, belt retractor sensor and belt tensioner are mounted in a unit. If there is a fault in any of these components, the entire unit must be replaced.
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 sensors comprise a Hall sensor that changes current strength based on the position of the seat. The seat position sensor has two classifications - small person or large person. Small person indicates that the seat is approx. 10 cm (4 in) or less from the front-most seat position. All other positions are classified as large person.
This information is used by the function for adaptive seatbelt force limiting.
Switch on/off, front passenger airbag (not USA/CDN)
With the switch it is possible to activate or deactivate the airbag for the front seat passenger.
The switch is located on the side of the instrument panel, on the passenger side. The switch is only accessible when the front side door on the passenger side is open.
The ignition key is used to change the position of the switch. When the switch is in position "OFF", all steps for the passenger airbag are deactivated and warning light airbag passenger (PAD) is lit.
When the switch is in position "ON", the passenger airbag is activated and warning light activated airbag passenger (PAE) is lit.
When the switch position is moved between "OFF" and "ON", two Hall sensor sense in which position the switch is. The Hall sensors for the switch are directly connected to the Supplemental restraint system module (SRS).
Each Hall sensor is separately connected to the control module. The signal that is sent from the Hall sensors consists of two different current levels depending on which position the switch is in.
If the signal from the Hall sensor cannot be interpreted correctly, a diagnostic trouble code is generated and the control module may, depending on the problem, choose to deactivate the passenger airbag.
If the passenger airbag is deactivated then warning light airbag passenger (PAD) and SRS-warning light are lit, and a text message is shown in the Driver information module (DIM). If a problem is detected and the passenger airbag is not deactivated, instead warning light activated airbag passenger (PAE) and the SRS-warning light are lit, and a text message is shown in the Driver information module (DIM).
Note! The activating switch, on/off, 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.
- 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 and occupant weight sensor are linked via a hose. The pressure sensor registers the pressure the seat cushion is exposed to, for example when someone is sitting in the seat.
Information from the seat belt force sensor is also used to ensure the good performance of the system. The seatbelt 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 seatbelt tightly. This means that the passenger exerts greater pressure on the seat than during normal seatbelt use. The passenger is then interpreted as being heavier than he or she is.
Using information from both the pressure sensor and the seat belt force sensor, the occupant weight sensor module carries out calculations and classifications of what is affecting the system. This forms the basis for the recommendation that is communicated to the supplemental restraint system.
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:
- disable the front passenger airbag
- light the passenger airbag warning lamp (PAD) in the roof console
- light the SRS (supplemental restraint system) warning 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 activating switch, on/off, for the front passenger airbag and occupant weight sensor (OWS) must not be installed in the vehicle together.
Adaptive seatbelt force limiter (USA/CDN only)
Warning! Never use an ohmmeter or similar tool to test airbags, inflatable curtains adaptive seatbelt limiters, adaptive steering column or seat belt tensioners. Disconnect airbags, inflatable curtains adaptive seatbelt limiters, adaptive steering column 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 belt force limiter improves the seat belt function in the event of a head-on collision when the airbag has been deployed. There are two adaptive belt force limiters in the car. These are located in top of the belt retractors, positioned at shoulder height on the driver's and front passenger seat belts.
The adaptive seatbelt force limiters are electrically separated from each other. The adaptive seatbelt force limiters have a pyrotechnic charge which adapts the seatbelt force to a lower level against the chest on activation.
The adaptive belt force limiter, belt retractor, belt retractor sensor and belt tensioner are mounted in a unit. If there is a fault in any of these components, the entire unit must be replaced.
The adaptive belt force limiter and lap belt tensioner use the same connections on the supplemental restraint system module (SRS). Thus, they cannot be connected at the same time in the vehicle.
Adaptive steering column (USA/CDN only)
Warning! Never use an ohmmeter or similar tool to test airbags, inflatable curtains adaptive seatbelt limiters, adaptive steering column or seat belt tensioners. Disconnect airbags, inflatable curtains adaptive seatbelt limiters, adaptive steering column 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 adaptive steering column in the collision protection system is activated, a pin is deployed which makes the steering column longitudinally adjustable and thus collapsible. If the frontal collision exceeds a certain level the steering wheel is pressed into the dashboard to a greater degree than if the steering column were 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 functions if the driver is wearing the seatbelt and if the airbag deploys. The entire steering column must be replaced if the collision protection system in the adaptive steering column has deployed.