Dodge dakota 2002 Service Manual page 655

8O - 54 RESTRAINTS
SIDE IMPACT AIRBAG CONTROL MODULE (Continued)
(SIACM) and its mounting bracket are secured with
four screws to the inside of each B-pillar behind
(standard cab) or above (quad cab) the front outboard
seat belt retractor, and concealed behind the B-pillar
trim (Fig. 50). Concealed within a hollow in the cen-
ter of the die cast aluminum SIACM housing is the
electronic circuitry of the SIACM which includes a
microprocessor and an electronic impact sensor.
The SIACM housing is secured to a die cast (stan-
dard cab) or stamped steel (quad cab) mounting
bracket, which is unique for the right or left side
application of this component. The SIACM should
never be removed from its mounting bracket. The
housing also receives a case ground through this
mounting bracket when it is secured to the vehicle. A
molded plastic electrical connector receptacle that
exits the top of the SIACM housing connects the unit
to the vehicle electrical system through a dedicated
take out and connector of the body wire harness.
Both the SIACM housing and its electrical connection
are sealed to protect the internal electronic circuitry
and components against moisture intrusion.
The impact sensor internal to the SIACM is cali-
brated for the specific vehicle, and is only serviced as
a unit with the SIACM. The SIACM cannot be
repaired or adjusted and, if damaged or faulty, it
must be replaced.
OPERATION
The microprocessor in the Side Impact Airbag Con-
trol Module (SIACM) contains the side curtain airbag
system logic circuits and controls all of the features
of only the side curtain airbag mounted on the same
side of the vehicle as the SIACM. The SIACM uses
On-Board Diagnostics (OBD) and can communicate
with other electronic modules in the vehicle as well
as with the DRBIII scan tool using the Programma-
ble Communications Interface (PCI) data bus net-
work. This method of communication is used by the
SIACM to communicate with the Airbag Control
Module (ACM) and for supplemental restraint system
diagnosis and testing through the 16-way data link
connector located on the driver side lower edge of the
instrument panel. The ACM communicates with both
the left and right SIACM over the PCI data bus.
The SIACM microprocessor continuously monitors
all of the side curtain airbag electrical circuits to
determine the system readiness. If the SIACM
detects a monitored system fault, it sets an active
and stored Diagnostic Trouble Code (DTC) and sends
electronic messages to the ACM over the PCI data
bus. The ACM will respond by sending an electronic
message to the EMIC to turn on the airbag indicator,
and by storing a DTC that will indicate whether the
left or the right SIACM has stored the DTC that ini-
tiated the airbag indicator illumination. An active
fault only remains for the current ignition switch
cycle, while a stored fault causes a DTC to be stored
in memory by the SIACM. For some DTCs, if a fault
does not recur for a number of ignition cycles, the
SIACM will automatically erase the stored DTC. For
other internal faults, the stored DTC is latched for-
ever.
The SIACM receives battery current on a fused
ignition switch output (run-start) circuit through a
fuse in the Integrated Power Module (IPM). The
SIACM has a case ground through its mounting
bracket and also receives a power ground through a
ground circuit and take out of the body wire harness.
This take out has a single eyelet terminal connector
that is secured by a ground screw to the body sheet
metal. These connections allow the SIACM to be
operational whenever the ignition switch is in the
Start or On positions. An electronic impact sensor is
contained within the SIACM. The electronic impact
sensor is an accelerometer that senses the rate of
vehicle deceleration, which provides verification of
the direction and severity of an impact. A pre-pro-
grammed decision algorithm in the SIACM micropro-
cessor determines when the deceleration rate as
signaled by the impact sensor indicates a side impact
that is severe enough to require side curtain airbag
protection. When the programmed conditions are
met, the SIACM sends the proper electrical signals to
deploy the side curtain airbag.
The hard wired inputs and outputs for the SIACM
may be diagnosed and tested using conventional
diagnostic tools and procedures. However, conven-
tional diagnostic methods will not prove conclusive in
the diagnosis of the SIACM, the PCI data bus net-
work, or the electronic message inputs to and outputs
from the SIACM. The most reliable, efficient, and
accurate means to diagnose the SIACM, the PCI data
bus network, and the electronic message inputs to
and outputs from the SIACM requires the use of a
DRBIII scan tool. Refer to the appropriate diagnos-
tic information.
DR