Part 2

Design (Continued)

Side impact air bags

XC90

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 configuration, there are up to four inflatable curtains connected to the supplemental restraint system module (SRS). Their connectors are electrically separated from each other.
For the 7 seater XC90 models, the inflatable curtains are in the roof between the A and D-posts. For the 5 seater XC90 models and other models, the inflatable curtains are in the roof between the A and C-posts.
The configuration is as follows:
- On the 7 seater XC90, side and rear inflatable curtains on each side. There are a total of four inflatable curtains
- On the 5 seater XC90 and other models, there is one inflatable curtain on each side. There are a total of two inflatable curtains.
The inflatable curtains have only one ignition component each. The task of the inflatable curtains is to protect the head and the upper body in the event of a side impact. The supplemental restraint system module (SRS) activates the inflatable curtains on the side where the collision occurred.
The inflatable curtain uses 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 inflatable curtain which falls and covers the side windows and B post. If rear inflatable curtains are installed the C post is also covered.
Where there are two inflatable curtains per side, these are always activated simultaneously.

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.

SRS indication
The supplemental restraint system module (SRS) continuously checks the system. A diagnostic trouble code (DTC) is stored and an SRS indication is made.
SRS indication is accompanied by a text message in the Driver information module (DIM), partly through:
- an SRS warning lamp
- a general warning lamp.
The lamps light depending on how serious the fault is: Information about which lamp should be lit is transmitted by the supplemental restraint system module (SRS) on the controller area network (CAN).
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 on the controller area network (CAN) to the driver information module (DIM) confirming that the SRS indicator lamp can be switched off. If no faults are detected when the ignition is switched on, the lamp will remain lit for a few seconds. The lamp goes out when the system has been checked and is operating without faults.
The control module has an EEPROM memory which retains data about diagnostic trouble codes (DTCs) even when the battery has been disconnected.
The driver information module (DIM) continuously indicates to the supplemental restraint system module (SRS) the function of the SRS indicator lamp. If the lamp stops working, the general warning lamp lights up and a text message is displayed.

Note! If a diagnostic trouble code (DTC) is stored because the resistance in an SRS ignition cable is too high or too low, it is important that the resistance of the SRS ignition cable is not measured when the collision protection system is connected. Special tools with the same resistance as the collision protection system must be used for fault-tracing.

Passenger airbag indication

Supplemental restraint system module (SRS) transmits signals on the CAN network to the upper electronic module (UEM) if the front passenger airbag is activated or not. If the upper electronic module (UEM) receives information that the passenger airbag is deactivated, the upper electronic module (UEM) lights the passenger airbag warning lamp (PAD). The warning lamp is located in the upper section of the rear view mirror.
Depending on the market, if the switch for activating and deactivating the front passenger airbag is used to deactivate it, the passenger airbag disconnected (PAD) warning lamp lights.
The warning lamp goes out when the airbag is reactivated.
If an occupant weight sensor (OWS) is installed (market and model dependent), the passenger airbag disconnected (PAD) warning lamp lights when the airbag is deactivated. However there is an exception to this:
- The passenger airbag disconnected warning lamp will remain unlit if the occupant weight sensor (OWS) registers that the passenger seat is unoccupied. This means that the passenger airbag is deactivated.
The warning lamp goes out when the airbag is reactivated.
Reasons that the passenger airbag disconnected warning lamp lights may also be:
- communication problems between the supplemental restraint system module (SRS) and upper electronic module (UEM)
- faulty function in the on/off switch for the front passenger airbag
- defective occupant weight sensor (OWS) function.

Seat belt buckle

The two front seat belt buckles have Hall sensors and are connected to the SRS module. These connections are electrically separated from each other.
The hall sensor detects whether the belt is engaged in the seat belt buckle or not and indicates this to the supplemental restraint system module (SRS). The information is used to set the activation level for the airbags and seat belt tensioners. If a fault is detected in the seat belt buckles or in their terminals, an adjustment is made for this, depending on the type of fault.

Activating the collision protection system
The collision safety system is extremely advanced. It is able to adapt the collision protection system to suit the specific circumstances of a collision. In general it is extremely unlikely that all airbags and seat belt tensioners will be deployed in the same accident. It is possible that only one airbag or seat belt tensioner is deployed. This is determined by the supplemental restraint system module (SRS) based on the forces that occur during the collision.
If the control module deploys the front airbags, all stages will always be activated. By varying the time between the deployment phases, the inflation of the airbag is more gentle for a low speed collision.

Activation levels for the collision protection system
The table below shows how the SRS system reacts in the event of a frontal impact.
Level 1= Low speed collision
Level 5 = Severe collision

Activating the side impact protection system
The table below shows how the SRS system reacts in the event of a side impact.