This is from a 2003 KJ Service Manual on the two front airbag impact sensors. It looks they are around the radiator support (left and right). Then there is also the airbag control module (which I also included at the end). Wow! Something else...
FRONT IMPACT SENSOR
Two front impact sensors are used on this model,
one each for the left and right sides of the vehicle
(Fig. 19). These sensors are mounted remotely from
the impact sensor that is internal to the Airbag Control
Module (ACM). Each front sensor is secured with
two screws to the backs of the right and left vertical
members of the radiator support within the engine
compartment. The sensor housing has an integral
connector receptacle and two integral mounting
points each with a metal sleeve to provide crush protection.
The right and left front impact sensors are identical
in construction and calibration with two exceptions.
On models equipped with an optional 2.4L
gasoline engine or an optional 2.5L diesel engine, the
left front impact sensor includes a stamped metal
mounting bracket that rotates the connector receptacle
end of the sensor toward the outboard side of the
vehicle for additional clearance that is required for
those applications.
A cavity in the center of the molded black plastic
impact sensor housing contains the electronic circuitry
of the sensor which includes an electronic communication
chip and an electronic impact sensor.
Potting material fills the cavity to seal and protect
the internal electronic circuitry and components. The
front impact sensors are each connected to the vehicle
electrical system through a dedicated take out
and connector of the headlamp and dash wire harness.
The impact sensors cannot be repaired or adjusted
and, if damaged or faulty, they must be replaced. On
models equipped with an optional 2.4L gasoline
engine or an optional 2.5L diesel engine, the mounting
bracket for the left front impact sensor is serviced
as a unit with that sensor.
OPERATION
The front impact sensors are electronic accelerometers
that sense the rate of vehicle deceleration,
which provides verification of the direction and severity
of an impact. Each sensor also contains an electronic
communication chip that allows the unit to
communicate the sensor status as well as sensor
fault information to the microprocessor in the Airbag
Control Module (ACM). The ACM microprocessor continuously
monitors all of the front passive restraint
system electrical circuits to determine the system
readiness. If the ACM detects a monitored system
fault, it sets a Diagnostic Trouble Code (DTC) and
controls the airbag indicator operation accordingly.
The impact sensors each receive battery current
and ground through dedicated left and right sensor
plus and minus circuits from the ACM. The impact
sensors and the ACM communicate by modulating
the voltage in the sensor plus circuit. The hard wired
circuits between the front impact sensors and the
ACM may be diagnosed and tested using conventional
diagnostic tools and procedures. However, conventional
diagnostic methods will not prove
conclusive in the diagnosis of the ACM or the impact
sensors. The most reliable, efficient, and accurate
means to diagnose the impact sensors, the ACM, and
the electronic message communication between the
sensors and the ACM requires the use of a DRBIIIt
scan tool.
AIRBAG CONTROL MODULE
OPERATION
The microprocessor in the Airbag Control Module
(ACM) contains the front supplemental restraint system
logic circuits and controls all of the front supplemental
restraint system components. The ACM uses
On-Board Diagnostics (OBD) and can communicate
with other electronic modules in the vehicle as well
as with the DRBIIIt scan tool using the Programmable
Communications Interface (PCI) data bus network.
This method of communication is used for
control of the airbag indicator in the ElectroMechanical
Instrument Cluster (EMIC) 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. (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER/AIRBAG
INDICATOR - OPERATION).
The ACM microprocessor continuously monitors all
of the front supplemental restraint system electrical
circuits to determine the system readiness. If the
ACM 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, 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
forever.
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 buckled,
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 optional side
curtain airbags, the ACM communicates with both
the left and right Side Impact Airbag Control Modules
(SIACM) over the PCI data bus. The SIACM
notifies the ACM when it has detected a monitored
system fault and stored a DTC in memory for its
respective side curtain airbag system, and the ACM
sets a DTC and controls the airbag indicator operation
accordingly.
The ACM receives battery current through two circuits;
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 has a case
ground through a lug on the bottom of the ACM
housing that is secured with a ground screw to the
left side of the ACM mounting bracket. The ACM
also receives a power ground through a ground circuit
and take out of the instrument panel wire harness.
This take out has a single eyelet terminal
connector that is secured by a second ground screw
to the left side of the ACM mounting bracket. These
connections allow the ACM to be operational whenever
the ignition switch is in the Start or On positions.
The ACM also contains an energy-storage capacitor.
When the ignition switch is in the Start or On
positions, this capacitor is continually being charged
with enough electrical energy to deploy the front supplemental
restraint components for up to one second
following 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 direction
and severity of an impact.
The safing sensor is an electromechanical 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 front supplemental
restraint deployment by detecting impact energy of a
lesser magnitude than that of the electronic impact
sensors, and must be closed in order for the front airbags
or the seat belt tensioner to deploy.
A pre-programmed decision algorithm in the ACM
microprocessor determines when the deceleration
rate as signaled by the impact sensors and the safing
sensor indicate an impact that is severe enough to
require front supplemental restraint system protection
and, based upon the status of the driver side
front seat belt switch input and the severity of the
monitored impact, determines what combination of
driver seat belt tensioner and front airbag deployment
is required for each front seating position.
When the programmed conditions are met, the ACM
sends the proper electrical signals to deploy the
driver seat belt tensioner and the dual multistage
front airbags at the programmed force levels.
The hard wired inputs and outputs for the ACM
may be diagnosed and tested using conventional
diagnostic tools and procedures. However, conventional
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 network,
and the electronic message inputs to and outputs
from the ACM requires the use of a DRBIIIt
scan tool. Refer to the appropriate diagnostic information.
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