Jaguar XJ (X350). Manual — part 1564

4

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Side airbag module

5

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B-Pillar side impact sensor

6

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C-Pillar side impact sensor

7

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Front safety belt pretensioner

8

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Front passenger seat occupant classification sensor

Sensors

WARNING: Prior to the removal of any SRS sensors and before disconnecting

any SRS sensor electrical connectors, the battery ground cable must be disconnected
and a period of one minute allowed to elapse.

NOTE:

The SRS sensors do not contain any serviceable components.

The SRS consists of the following sensors:

Occupant Position Sensors

The four sensors are strategically placed to detect the presence and movement of the
passenger front seat occupant.

The occupant position sensor system uses ultrasound at an operating frequency of 40 kilohertz
to monitor the passenger front seat occupant. The SRS uses four ultrasonic sensors, one in the
A-pillar, one at the top of the instrument panel console and two in the headliner. The sensors
determine the presence and position of the passenger front seat occupant with respect to the
passenger air bag deployment door. The sensors determine passenger air bag module
deployment decisions by classifying occupants as either 'in position' or 'out of position'
according to the predetermined 'keep out zone'. The sensors are part of a system that is
sophisticated enough to be unaffected by body extremities (hands and feet) and respond only
to head or body movements.

Front Crash Sensor

The crash sensor is attached to the body behind the radiator grille. The restraints control
module (RCM) processes the crash data sent by the crash sensor against stored data, and
deploys the front air bags and pretensioners.

Side Impact Sensors

The side impact sensors are mounted at the base of the B-pillars and C-pillars to facilitate
lateral impact sensing. In the event of a side impact, the RCM processes the crash data against
the stored data. The RCM will deploy the side air bag module and side air curtain module on
the side the deployment request was initiated.

Seat Position Sensor

The seat position sensor is located on the driver seat track. The seat position sensor
determines the position of the driver seat, which is then communicated to the RCM. If the
driver seat is in the forward position, the driver air bag module second stage is disabled.

Front Passenger Seat Occupant Classification Sensor

NOTE:

The front seat occupant classification sensor is serviced as a calibrated assembly.

Individual components of the front seat passenger weight sensing system are not serviceable.
The system must be replaced as a complete unit and due to its sophistication, each
replacement system requires calibration. To avoid the need to provide calibration equipment
to each dealer, a pre-calibrated service kit is available. The following components are
combined and calibrated during manufacture to form the front seat passenger weight sensing
system:

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Passenger seat cushion

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Silicone filled bladder

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Weight sensing control module

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Pressure sensor

The weight sensing control module is mounted under the passenger front seat. The silicone
filled bladder is integrated into the seat cushion and the pressure sensor, which is attached to
the bladder, is mounted under the seat.

The silicone filled bladder responds to weight changes on the passenger front seat. The
pressure sensor responds to these pressure changes and provides an appropriate signal to the
weight sensing control module. The weight sensing control module processes the input signal
received from the pressure sensor and makes it available to the RCM via the controller area
network (CAN). In addition, the weight sensing control module performs self-diagnostic
functions on the system, with any malfunctions being notified to the RCM accordingly.

The front seat passenger weight sensing system responds to the occupancy of the passenger
front seat in accordance with the following:

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Passenger front seat status 'EMPTY' — Passenger air bag status 'OFF' — Passenger
Air Bag Deactivation (PAD) indicator 'OFF'

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Passenger front seat status 'OCCUPIED' (small occupant) — Passenger air bag status
'OFF' — PAD indicator 'ON'

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Passenger front seat status 'OCCUPIED' (large occupant) — Passenger air bag status
'ON' — PAD indicator 'OFF'. PAD indicator 'ON' if the occupant position sensor
detects an occupant out of position

The SRS via the RCM, monitors and processes data from the front seat passenger weight
sensing system and several other sensors before making a deployment decision. Malfunction
of the sensing system or associated circuits will cause the SRS indicator to illuminate.

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Front Safety Belt Buckle Sensors

The safety belt buckle sensor is a 'hall effect' type sensor which provides an output signal in
response to the magnetic field disturbance caused by the insertion of the safety belt tongue
into the buckle. The output signal from the sensor is used by the RCM to determine whether
the front seat occupants are correctly restrained. It is used in conjunction with other
components of the SRS to ensure that air bag module and safety belt pretensioner deployment
only occurs where necessary. For additional information, refer to Safety Belt System (501-
20A)
Malfunction of the sensor or associated circuits will cause the SRS indicator to illuminate.

Modules

WARNING: Prior to the removal of any SRS module and before disconnecting

any SRS module electrical connectors, the battery ground cable must be disconnected
and a period of one minute allowed to elapse.

NOTE:

The SRS modules do not contain any serviceable components.

The SRS consists of the following modules:

Restraints Control Module (RCM)

The RCM is mounted on the top of the drive shaft tunnel below the instrument panel console.
It identifies crash severity, the direction of impact and makes decisions on deployment of air
bag modules and safety belt pretensioners. It also provides firing signals to all air bag
modules and safety belt pretensioners.

The RCM controls air bag deployment decisions by using signals from its internal
accelerometer and the following:

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Crash sensor

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Side impact sensors

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Occupant position sensors

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Front safety belt buckle sensor

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Seat position sensor

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Front passenger seat occupant classification system

Internally, the RCM has two areas that determine which elements of the SRS are to be
deployed:

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Crash severity evaluation — This area evaluates crash severity by using data from the
RCM internal accelerometer, the front crash sensor and the safety belt buckle sensor.
Based on this data, the RCM decides which level of air bag module deployment is
required and forwards the information to the second area, the deployment handler.

•

Deployment handler — The status of the seat track position sensor, occupant position
sensors, front passenger seat occupant classification sensor and safety belt buckle
sensors are examined before a decision is made about which restraints should finally
be deployed. For instance, if the occupant position sensors and front passenger seat
occupant classification sensor indicate that the front passenger seat is empty, then no
restraint deployment will take place on the passenger side, even if full deployment
takes place on the driver side.

Data from the side crash sensors is used by the RCM in conjunction with acceleration data
from the RCM internal accelerometer to make a deployment decision. The RCM processes
the acceleration data and subject to an impact being of high enough severity, decides whether
the side air bag module should be deployed. The decision is forwarded to the deployment
handler (within the RCM) which responds appropriately. For example, in the case that the
front passenger seat occupant classification sensor calculates that the seat is empty, or
occupied by a small person, the front or passenger side air bag module will be disabled.

On board testing of the air bag modules, front safety belt pretensioner firing circuits, warning
indicator circuits and module status (the crash and side impact sensors perform basic self-
tests) is performed by the RCM together with the storing of fault codes.

The RCM drives the SRS indicator on the instrument pack. If the warning lamp fails, a fault
code is recorded and a warning tone is sounded. It also provides a temporary back-up power
supply to operate the air bag modules in the event that in crash conditions, the battery supply
is lost. In the event of a crash, it records certain data which can be accessed via the diagnostic
connector.

Driver Air Bag Module

NOTE:

Variation in the driver air bag module deployment is determined by the timing of the first
and second stage ignition signals. This facilitates adaptation of the stiffness and timing of
the air bag module to optimize occupant protection.

The driver air bag module is controlled by the RCM which chooses between first or second
stage deployment, depending on the occupant position and the crash severity. To reduce the
risk of an air bag module induced injury to a driver that is positioned close to the steering
wheel, the air bag module deploys radially. It has a non-azide propellant that reduces
particulates and effluents. It consists of a two stage inflator with separate chambers for the
two inflation stages, each being independently activated by the RCM. It has two electrical
connectors that are color coded to the respective connector on the inflator.

Passenger Air Bag Module

NOTE:

Variation in the passenger air bag module deployment is determined by the timing of the
first and second stage ignition signals. This facilitates adaptation of the stiffness and
timing of the air bag module to optimize occupant protection.

The passenger air bag module is controlled by the RCM which chooses between first or

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