JAGUARS-TYPE
D.418.233
Occupant Protection
36
Restraints Control Module (RCM)
The RCM:
¥ Houses the electro-mechanical safing sensor
and electronic discrimination sensor which
detect a frontal impact.
¥ Houses the electronic safing sensor to detect
a side impact.
¥ Identifies severity and direction of impact
and makes decision on deployment of airbags
and pre-tensioners.
¥ Provides firing signals to all airbags and pre-
tensioners.
¥ Performs on board testing of the airbag and
pretensioner firing circuits, warning indicator
circuits and module status (Side Impact
Sensor performs its own internal checks).
¥ Stores fault codes in non-volatile memory.
¥ Drives the airbag warning lamp on the
instrument pack: if the warning lamp is
faulty (fault code recorded) an audible
warning tone is sounded.
¥ In the event of an impact, sends a signal to
the vehicle emergency message system
(VEMS) and the PCM to indicate that a crash
has occurred.
¥ Is connected to the data link connector via
the SCP data bus to enable communication
with an external PDU or scan tool.
¥ Provides temporary back-up power to operate
the airbags in the event of loss of battery
supply in an impact.
¥ In the event of an impact, records certain
data for subsequent access via the data link
connector. This data includes deceleration
information, firing delay and fault codes.
The RCM is bolted to the top of the driveshaft
tunnel below the center stack. Due to the
importance of the module being securely fixed to
the vehicle body, the ground connection is made
via the fixing bolts and is monitored by the
diagnostic system. A bad connection causes a fault
code to be generated.
Note:The torque settings are safety critical and
the figures given in the JTIS Service instructions
must be adhered to. RESTRAINTS CONTROL MODULE
D.418.233
detection signal received from either the LH or RH
Side Impact Sensor in order to deploy the
corresponding airbag.
Note:An impact at an oblique angle may cause
both frontal and side airbags to deploy, depending
on how much lateral acceleration is sensed.
JAGUARS-TYPEOccupant Protection
37
D.418.445
SIDE IMPACT SENSORSide Impact Sensor
The side impact sensors are mounted on brackets
attached to each inner sill.
The side impact sensor contains an electronic
discriminator sensor which detects side impacts
above a set threshold and signals a deployment
request to the RCM. Bag deployment only occurs
if the side safing sensor in the RCM has also
detected an impact.
The side impact sensor monitors its own internal
state, including correct ground connection, and
sends a regular ÔheartbeatÕ signal to the RCM
indicating that it is functioning correctly and is
available.
A 2 wire cable is connected between the RCM
and the side impact sensor. The cable has a dual
function, supplying power to the side impact
sensor and transmitting digital data to the RCM.
Diagnostics
The restraints control module (RCM) performs all
SRS diagnostics except those relating to the side
impact sensor internal faults and grounding faults.
When the ignition is switched on, the RCM carries
out a system Ôprove outÕ over an 8 second period
during which the airbag warning lamp on the
instrument pack is lit for the first 6 seconds.
During the prove out period all circuits connected
to the RCM are tested and also the state of the
RCM and side impact sensors (including ground
resistance and supply voltage).
If no faults are detected, the airbag warning lamp
remains off after the 8 second period.
If a fault is detected the warning lamp flashes a
two digit code five times and then remains lit until
the ignition is switched off. This is repeated on
each ignition cycle until the fault is cleared. Fault
codes are allocated a priority and if more than
one fault is stored in the RCM memory, the
highest priority fault is flashed. When this fault is
rectified, the next priority fault is indicated.
If the warning lamp itself is inoperative, the RCM
stores a fault code but no other action occurs. If a
system fault occurs when the lamp is inoperative,
a five ÔbleepÕ audible warning is sounded five
times with 5 second intervals. The audible
warning is repeated every 30 minutes and on
subsequent ignition cycles until the fault is
cleared.
If no faults are found during the system prove out
period the RCM continues to test the SRS system
during the remainder of the ignition cycle.Fault diagnosis of the side impact sensor is
normally carried out using the portable diagnostic
unit (PDU). Where the PDU is not available, the
flashing code on the airbag warning lamp indicates
the likely circuit or component fault.
