Part 2

Occupant weight sensor (OWS) (certain markets and models only)

The occupant weight sensor (OWS) consists of three interactive components:
- The pressure sensor, installed under the front passenger seat
- The seatbelt 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 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 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. The occupant weight sensor module uses the information from both the pressure sensor and seatbelt force sensor to calculate the actual weight of the passenger. The occupant weight sensor (OWS) transmits continuous signals to the supplemental restraint system module (SRS) and occupant weight sensor (OWS) on the LIN bus. 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 upper electronic module (UEM)
- 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 seatbelt 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.

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. When the switch is moved between OFF and ON, the two Hall sensors detect the position of the switch. 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 lights if the passenger airbag is deactivated. If a fault is detected and the passenger airbag is not deactivated, the SRS warning 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.

Front airbags

Driver airbag

Front passenger airbag

Warning! Never use an ohmmeter or similar tool to test airbags, inflatable curtains, the adaptive steering column or seat belt tensioners. Disconnect airbags, inflatable curtains, the 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.

For the XC90 in USA/CDN, the front airbags are:
- driver airbag, 3 stage deployment
- front passenger airbag, 3 stage deployment.
For other models and markets, the front airbags 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.
Each airbag stage has a separate ignition. 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.
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 and mixes with the stored gas. The gas mixture is blown into 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 is blown into the airbag.
The pace of the airbag 2 stage activation is dependent on collision type and seat belt use. Both stages activate but 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.

Stage 3 (XC90 USA/CDN only)
Stage 3 of the driver's and passenger airbags is pyrotechnical. A valve opens on the airbag during deactivation.
The control module uses information from the occupant weight sensor (OWS), seat position sensor and collision sensor to determine the size of the driver/passenger and the force of the collision. The control module adapts the volume of the airbag to the force of the collision. This is done using airbag ventilation.

Warning! Never use an ohmmeter or similar tool to test airbags, inflatable curtains, the adaptive steering column or seat belt tensioners. Disconnect airbags, inflatable curtains, the 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.

Side impact air bags

Warning! Never use an ohmmeter or similar tool to test airbags, inflatable curtains, the adaptive steering column or seat belt tensioners. Disconnect airbags, inflatable curtains, the 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.

Depending on the model and market, there may be up to seven seat belt tensioners in the vehicle. Two in the front seat, three in the rear seats and two in the third row if applicable. The seat belt tensioners contain an explosive charge which tensions the seat belts when deployed. The seat belt tensioners are separated from each other electrically. This means that each seat belt tensioner has a separate individual power supply and ground from the control module.
The seat belt tensioner tensions the seat belt to reduce the forward movement of the body. This also reduces the forces on the chest from the airbag and seat belt.
The supplemental restraint system module (SRS) determines whether to deploy the seat belt tensioners based on whether the seat belts are being used. The seat belt tensioner will not be activated if the seat belt is not engaged. If the seat belt is fastened and the seatbelt indication does not function for the front seat belt buckles, the seat belt tensioners will be activated anyway.
The seat belt tensioner consists of a pyrotechnical charge and a cylinder with a piston. The piston is connected to a steel cable which is secured to the seat belt reel. When the control module activates the seat belt tensioner the piston is forced downwards by the expanding gas. The piston pulls in the steel cable which reels in the belt.

Warning! Never use an ohmmeter or similar tool to test airbags, inflatable curtains, the adaptive steering column or seat belt tensioners. Disconnect airbags, inflatable curtains, the 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.