Jeep KJ 2005 Service Manual page 587

8O - 12 RESTRAINTS
AIRBAG CONTROL MODULE (Continued)
detects a monitored system fault, it sets an active
and stored Diagnostic Trouble Code (DTC) and sends
electronic messages to the EMIC over the PCI data
bus to turn on the airbag indicator. An active fault
only remains for the duration of the fault, or in some
cases for the duration of the current ignition switch
cycle, while a stored fault causes a DTC to be stored
in memory by the ACM. For some DTCs, if a fault
does not recur for a number of ignition cycles, the
ACM will automatically erase the stored DTC. For
other internal faults, the stored DTC is latched for-
ever.
The ACM also monitors a Hall effect-type seat belt
switch located in the buckle of the driver side front
seat belt to determine whether that seat belt is buck-
led, and provides an input to the EMIC over the PCI
data bus to control the seatbelt indicator operation
based upon the status of the driver side front seat
belt switch.
On models equipped with the Occupant Classifica-
tion System (OCS), the ACM communicates with the
Occupant Classification Module (OCM) over the PCI
data bus. The ACM stores OCS calibration data for
retrieval when the OCM must be replaced with a
new unit. The ACM will internally disable the pas-
senger airbag and seat belt tensioner deployment cir-
cuits if the OCM detects that the passenger side
front seat is unoccupied or that it is occupied by a
load that is inappropriate for an airbag deployment.
The ACM also provides a control output to the pas-
senger airbag on/off indicator through the passenger
airbag on/off indicator driver circuit. The OCM noti-
fies the ACM when it has detected a monitored sys-
tem fault and stored a DTC in its memory for any
faulty OCS component or circuit, then the ACM sets
a DTC and controls the airbag indicator operation
accordingly.
The ACM receives battery current through two cir-
cuits; a fused ignition switch output (run) circuit
through a fuse in the Junction Block (JB), and a
fused ignition switch output (run-start) circuit
through a second fuse in the JB. The ACM receives
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 top of the right front seat riser on the floor
panel beneath the right front seat. These connections
allow the ACM to be operational whenever the igni-
tion switch is in the Start or On positions.
The ACM also contains an energy-storage capaci-
tor. When the ignition switch is in the Start or On
positions, this capacitor is continually being charged
with enough electrical energy to deploy the supple-
mental restraint components for up to one second fol-
lowing a battery disconnect or failure. The purpose of
the capacitor is to provide backup supplemental
restraint system protection in case there is a loss of
battery current supply to the ACM during an impact.
Two sensors are contained within the ACM, an
electronic impact sensor and a safing sensor. The
ACM also monitors inputs from two remote front
impact sensors located on the back of the right and
left vertical members of the radiator support near
the front of the vehicle. The electronic impact sensors
are accelerometers that sense the rate of vehicle
deceleration, which provides verification of the direc-
tion and severity of an impact. On vehicles equipped
with optional side curtain airbags the ACM also mon-
itors inputs from two additional remote impact sen-
sors located on the left and right inner B-pillars to
control deployment of the side curtain airbag units.
The safing sensor is an electronic accelerometer
sensor within the ACM that provides an additional
logic input to the ACM microprocessor. The safing
sensor is used to verify the need for a supplemental
restraint deployment by detecting impact energy of a
lesser magnitude than that of the primary electronic
impact sensors, and must exceed a safing threshold
in order for the airbags to deploy. Vehicles equipped
with optional side curtain airbags, feature a second
safing sensor within the ACM to provide confirma-
tion to the ACM microprocessor of side impact forces.
This second safing sensor is a bi-directional unit that
detects impact forces from either side of the vehicle.
Pre-programmed decision algorithms in the ACM
microprocessor determine when the deceleration rate
as signaled by the impact sensors and the safing sen-
sors indicate an impact that is severe enough to
require supplemental restraint system protection
and, based upon the severity of the monitored
impact, determines the level of front airbag deploy-
ment force required for each front seating position.
When the programmed conditions are met, the ACM
sends the proper electrical signals to deploy the dual
multistage front airbags at the programmed force
levels, the front seat belt tensioners and, if the vehi-
cle is so equipped, either side curtain airbag unit.
For vehicles equipped with the OCS, the passenger
front airbag and seat belt tensioner will be deployed
by the ACM only if enabled by the OCM (passenger
airbag on/off indicator Off) at the time of the impact.
The hard wired inputs and outputs for the ACM
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 ACM, the PCI data bus network,
or the electronic message inputs to and outputs from
the ACM. The most reliable, efficient, and accurate
means to diagnose the ACM, the PCI data bus, and
the electronic message inputs to and outputs from
the ACM requires the use of a diagnostic scan tool.
Refer to the appropriate diagnostic information.
KJ