S60 AWD L5-2.5L Turbo VIN 59 B5254T2 (2005)
Air Bag Control Module: Description and Operation
Design
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 validates incoming pulsed collision signals (acceleration signals generated by a collision) and then determines the required
action. The control module uses internal sensors as well as external collision sensors. Using the data collected from the sensors, the system determines
which of the following will be activated:
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front airbags
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side impact protection (SIPS) bags
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inflatable curtains
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seat belt tensioners
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adaptive steering column (XC90 USA/CDN only).
The collision sensor in the control module registers the longitudinal mechanical stress that occurs in a frontal collision. A side impact may also be
registered in the collision sensor. The longitudinal stresses are measured using two acceleration sensors. On vehicles with front impact sensors, these are
used to register stresses in the event of a head-on collision. If the longitudinal stresses exceed a certain level, the stress will be calculated (the collision
pulse). The calculation evaluates whether the collision pulse was sufficient to activate the airbags and/or the seat belt tensioners. Airbags and seat belt
tensioners can be activated individually.
On the XC90, the control module is also able to register if the vehicle is about to roll over. If the sideways tilt and rotational energy of the car exceed a
certain level, the control module begins a calculation to determine whether the roll over protection should be activated. The critical tilt angle is 50-55
degrees. All seat belt tensioners and inflatable curtains are deployed if the roll over protection is activated.
For certain models, depending on the market, the following are also used:
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an occupant weight sensor (OWS) located under the seat cushion on the front passenger seat
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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. For the XC90
(USA/CDN only), the adaptive steering column will also be activated if necessary.
No seat belt tensioners or airbags will be activated in the event of a collision from the rear.
Two requirements need to be fulfilled in order for the side impact protection system to be activated:
1. that the collision pulse is sufficiently high that a trigger signal is sent from the side impact sensor to the control module
2. the control module or another collision sensor transmits a confirmation signal which allows the collision protection system to be deployed.
The side impact protection system is deployed when the control module has received both an activation and a confirmation signal.
If the side impact occurred at the front of the vehicle the side airbags and the inflatable curtains are deployed on the side that received the impact. If the
side impact is towards the rear of the car, only the inflatable curtains are deployed on that side.
