2002 JEEP GRAND CHEROKEE electronic control module

OPERATION
The power window system includes the Driver
Door Module (DDM) and Passenger Door Module
(PDM), which are mounted in their respective front
door, the rear door power window switches mounted
on the rear doors, and the power window motors
mounted to the window regulator in each door. The
DDM houses four master power window switches, the
power window lockout switch and the control logic for
the driver side front and rear door power windows.
The PDM houses the passenger side front door power
window switch and the control logic for the passenger
side front and rear door power windows.
When a master power window switch on the DDM
is used to operate a passenger side power window,
the DDM sends the window switch actuation mes-
sage to the PDM over the Programmable Communi-
cations Interface (PCI) data bus. The PDM responds
to these messages by sending control outputs to move
the passenger side power window motors. In addi-
tion, when the power window lockout switch in the
DDM is actuated to disable power window operation,
a lockout message is sent to the PDM over the PCI
data bus.
The Body Control Module (BCM) also supports and
controls certain features of the power window sys-
tem. The BCM receives a hard wired input from the
ignition switch. The programming in the BCM allows
it to process the information from this input and
send ignition switch status messages to the DDM
and the PDM over the PCI data bus. The DDM and
PDM use this information and hard wired inputs
from the front door ajar switches to control the light-
ing of the power window switch lamps, and to control
the operation of the power window after ignition-off
feature.
See the owner's manual in the vehicle glove box for
more information on the features, use and operation
of the power window system.
DIAGNOSIS AND TESTING - POWER
WINDOWS
Following are tests that will help to diagnose the
hard wired components and circuits of the power
window system. However, these tests may not prove
conclusive in the diagnosis of this system. In order to
obtain conclusive testing of the power window sys-
tem, the Programmable Communications Interface
(PCI) data bus network and all of the electronic mod-
ules that provide inputs to, or receive outputs from
the power window system components must be
checked.The most reliable, efficient, and accurate means to
diagnose the power window system requires the use
of a DRB scan tool and the proper Diagnostic Proce-
dures manual. The DRB scan tool can provide confir-
mation that the PCI data bus is functional, that all
of the electronic modules are sending and receiving
the proper messages on the PCI data bus, and that
the power window motors are being sent the proper
hard wired outputs by the door modules for them to
perform their power window system functions.
For complete circuit diagrams, refer to the appro-
priate wiring information. The wiring information
includes wiring diagrams, proper wire and connector
repair procedures, details of wire harness routing
and retention, connector pin-out information and
location views for the various wire harness connec-
tors, splices and grounds.
ALL WINDOWS INOPERATIVE
(1) Check the operation of the power lock switch
on the driver side front door. If all of the doors lock
and unlock, but none of the power windows operate,
use a DRB scan tool and the proper Diagnostic Pro-
cedures manual to check the Body Control Module
(BCM), the Driver Door Module (DDM) and the PCI
data bus for proper operation. If not OK, go to Step
2.
(2) Check the operation of the power lock switch
on the passenger side front door. If the passenger
doors lock and unlock, but the driver side front door
does not, go to Step 5. If all of the power locks and
power windows are inoperative from both front doors,
go to Step 3.
(3) Check the fused B(+) fuse in the Power Distri-
bution Center (PDC). If OK, go to Step 4. If not OK,
repair the shorted circuit or component as required
and replace the faulty fuse.
(4) Check for battery voltage at the fused B(+) fuse
in the PDC. If OK, go to Step 5. If not OK, repair the
open fused B(+) circuit to the battery as required.
(5) Disconnect and isolate the battery negative
cable. Remove the trim panel from the driver side
front door. Disconnect the 15-way door wire harness
connector from the DDM connector receptacle. Check
for continuity between the ground circuit cavity of
the 15-way door wire harness connector for the DDM
and a good ground. There should be continuity. If
OK, go to Step 6. If not OK, repair the open ground
circuit to ground as required.
(6) Reconnect the battery negative cable. Check for
battery voltage at the fused B(+) circuit cavity of the
15-way door wire harness connector for the DDM. If
OK, replace the faulty DDM. If not OK, repair the
open fused B(+) circuit to the fuse in the PDC as
required.
8N - 34 POWER WINDOWSWJ
POWER WINDOWS (Continued)

and no voltage in the neutral position. If OK,(Refer
to 8 - ELECTRICAL/POWER WINDOWS/WINDOW
MOTOR - DIAGNOSIS AND TESTING). If not OK,
replace the faulty door module.
(9) Check the rear door power window switch con-
tinuity. (Refer to 8 - ELECTRICAL/POWER WIN-
DOWS/POWER WINDOW SWITCH - DIAGNOSIS
AND TESTING). If OK, go to Step 10. If not OK,
replace the faulty rear door power window switch.
(10) Disconnect and isolate the battery negative
cable. Reconnect the door wire harness connector to
the rear door power window switch. Disconnect the
door wire harness connector from the inoperative
power window motor wire harness connector. Check
for continuity between the rear window driver up cir-
cuit cavity of the 15-way door wire harness connector
for the door module and a good ground. Repeat the
check for the rear window driver down circuit. In
each case there should be no continuity. If OK, go to
Step 11. If not OK, repair the shorted rear window
driver up or down circuit as required.
(11) Check for continuity between the rear window
driver up circuit cavities of the 15-way door wire har-
ness connector for the door module and the power
window motor wire harness connector. Repeat the
check for the rear window driver down circuit. In
each case there should be continuity. If OK, go to
Step 12. If not OK, repair the open rear window
driver up or down circuit as required.
NOTE: The door module feeds battery current to
both terminals of the rear door power window
motors when the power window lockout switch is in
the Unlock position, until the master window switch
on the driver side front door is actuated. The door
module feeds ground to both terminals of the rear
door power window motor when the power window
lockout switch is in the Lock position, until the
master window switch on the driver side front door
is actuated.
(12) Reconnect the 15-way door wire harness con-
nector for the door module to the door module con-
nector receptacle. Connect the battery negative cable.
Check for battery voltage at each cavity in the door
wire harness connector for the power window motor.
Each cavity should have battery voltage when the
power window switch is in the neutral position. Each
cavity should also have battery voltage in one other
switch position, either up or down, and zero volts
with the switch in the opposite position. If OK, (Refer
to 8 - ELECTRICAL/POWER WINDOWS/WINDOW
MOTOR - DIAGNOSIS AND TESTING). If not OK,
replace the faulty door module.POWER WINDOW SWITCH
DESCRIPTION
The power window motors are controlled by a two-
way momentary switch mounted on the trim panel of
each passenger door, and four two-way momentary
switches on the driver side front door trim panel. The
driver side front door trim panel also has a two-posi-
tion power window lockout switch. Each power win-
dow switch, except the lockout switch, is illuminated
by a Light-Emitting Diode (LED) that is integral to
the switch paddle.
The front door power window switches and the
power window lockout switch are integral to the
Driver Door Module (DDM) and Passenger Door
Module (PDM). The front door power window
switches and their lamps cannot be adjusted or
repaired and, if faulty or damaged, the entire DDM
or PDM unit must be replaced. The rear door power
window switches and their lamps cannot be adjusted
or repaired but, if faulty or damaged, only the
affected rear door power window switch must be
replaced. (Refer to 8 - ELECTRICAL/ELECTRONIC
CONTROL MODULES/DRIVER DOOR MODULE -
REMOVAL).
OPERATION
The front door power window switches provide an
up or down (or lock and unlock signal in the case of
the lockout switch) to the door module circuitry. The
Driver Door Module (DDM) circuitry controls the out-
put to the driver side front and rear door power win-
dow motors, and supplies electrical current as
required for the stand-alone operation of the driver
side rear door power window switch. The Passenger
Door Module (PDM) circuitry controls the output to
the passenger side front and rear door power window
motors, and supplies electrical current as required
for the stand-alone operation of the passenger side
rear door power window switch.
When a DDM-integrated master power window
switch for a passenger side window is actuated, or
when the power window lockout switch is actuated to
disable the passenger door power windows, the DDM
circuitry sends a message to the PDM over the Pro-
grammable Communications Interface (PCI) data bus
to control the output to that power window motor(s).
The power window switch for the driver side front
door power window has two detent positions in the
Down direction. The first detent provides normal
power window down operation. If this switch is
depressed to the second detent, the Auto Down cir-
cuitry of the DDM is activated. The Auto-Down cir-
cuitry will automatically move the driver side front
door window to its fully lowered position, even if the
power window switch is released. The Auto-Down
8N - 36 POWER WINDOWSWJ
POWER WINDOWS (Continued)

INSTALLATION
(1) Position the power window switch to the rear
door trim panel switch receptacle.
(2) Press firmly and evenly on the back of the
power window switch until it snaps into rear door
trim panel switch receptacle.
(3) Install the trim panel onto the rear door. (Refer
to 23 - BODY/DOORS - REAR/TRIM PANEL -
INSTALLATION) for the procedures.
(4) Reconnect the battery negative cable.
WINDOW MOTOR
DESCRIPTION
Power operated front and rear door windows are
standard equipment on this model. Each door has a
permanent magnet reversible electric motor with an
integral right angle gearbox mechanism that oper-
ates the window regulator. In addition, each power
window motor is equipped with an integral self-reset-
ting circuit breaker to protect the motor from over-
loads.
The power window motor gearbox housing is
secured to the window regulator drum housing with
screws. The window regulators used in all four doors
are single vertical post cable-and-drum type. A
molded plastic slider guided by the post is driven by
the regulator cables. The slider raises and lowers the
window glass through a steel lift plate attachment.
Front and rear glass channels within each door guide
and stabilize each end of the glass.
The power window motor and gearbox assembly
cannot be repaired and, if faulty or damaged, the
entire power window motor and gearbox unit must be
replaced. The window regulators are available for
service. (Refer to 23 - BODY/DOOR - FRONT/WIN-
DOW REGULATOR - REMOVAL) or (Refer to 23 -
BODY/DOORS - REAR/WINDOW REGULATOR -
REMOVAL) for the regulator service procedures.
OPERATION
A positive and negative battery connection to the
two motor terminals will cause the power window
motor to rotate in one direction. Reversing the cur-
rent through these same two connections will cause
the motor to rotate in the opposite direction.
When the power window motor operates, it rotates
the regulator cable drum through its gearbox. The
window regulator cable drum is connected through
two cables to the plastic slider on the vertical post.
As the cable drum rotates, it lets cable out on one
side of the drum, and takes cable in on the other side
of the drum. The changes in cable length move the
slider up or down the vertical post, raising or lower-
ing the window glass.If the window regulator or window glass bind,
encounter obstructions, or reach their travel limits it
overloads the power window motor. The overloading
condition causes the power window motor self-reset-
ting circuit breaker to open, which stops the motor
from running.
DIAGNOSIS AND TESTING - WINDOW MOTOR
Before you proceed with this diagnosis, confirm
proper switch operation. (Refer to 8 - ELECTRICAL/
ELECTRONIC CONTROL MODULES/DRIVER
DOOR MODULE - OPERATION) or (Refer to 8 -
ELECTRICAL/POWER WINDOWS/POWER WIN-
DOW SWITCH - OPERATION). For complete circuit
diagrams, refer to the appropriate wiring informa-
tion. The wiring information includes wiring dia-
grams, proper wire and connector repair procedures,
details of wire harness routing and retention, connec-
tor pin-out information and location views for the
various wire harness connectors, splices and grounds.
(1) Remove the trim panel from the door with the
inoperative power window. (Refer to 23 - BODY/
DOOR - FRONT/TRIM PANEL - REMOVAL) or
(Refer to 23 - BODY/DOORS - REAR/TRIM PANEL -
REMOVAL) for the procedures.
(2) Disconnect the door wire harness connector
from the power window motor wire harness connec-
tor. Apply battery current to one cavity of the power
window motor wire harness connector, and apply
ground to the other cavity of the connector. The
power window motor should operate in one direction.
Remember, if the window is in the full up or full
down position, the motor will not operate in that
direction by design. If OK, go to Step 3. If not OK,
replace the faulty power window motor.
(3) Reverse the battery and ground connections to
the two cavities of the power window motor wire har-
ness connector. The power window motor should now
operate in the other direction. Remember, if the win-
dow is in the full up or full down position, the motor
will not operate in that direction by design. If OK, go
to Step 4. If not OK, replace the faulty power window
motor.
(4) If the power window motor operates in both
directions, check the operation of the window glass
and regulator mechanism through its complete up
and down travel. There should be no binding or stick-
ing of the window glass or regulator mechanism
through the entire travel range. If not OK, (Refer to
23 - BODY/DOOR - FRONT/WINDOW REGULATOR
- REMOVAL) or (Refer to 23 - BODY/DOORS -
REAR/WINDOW REGULATOR - REMOVAL) to
check for proper installation or damage of the win-
dow glass mounting and operating hardware.
8N - 38 POWER WINDOWSWJ
POWER WINDOW SWITCH (Continued)

²Passenger Airbag- The passenger airbag is
located on the instrument panel, beneath the instru-
ment panel top pad and above the glove box on the
passenger side of the vehicle.
²Passenger Knee Blocker- The passenger knee
blocker is a structural reinforcement that is integral
to and concealed within the glove box door.
²Side Impact Sensor- Two side impact sensors
are used on vehicles with the optional side curtain
airbags, one left side and one right side. One sensor
is located behind the B-pillar trim near the base of
each B-pillar.
²Side Curtain Airbag- In vehicles equipped
with this option, a side curtain airbag is located on
each inside roof side rail above the headliner, and
extends from the A-pillar to just beyond the C-pillar.
The ACM and the EMIC each contain a central
processing unit and programming that allow them to
communicate with each other using the Programma-
ble Communication Interface (PCI) data bus network.
This method of communication is used by the ACM
for control of the airbag indicator on all models
equipped with dual front airbags. (Refer to 8 - ELEC-
TRICAL/ELECTRONIC CONTROL MODULES/
COMMUNICATION - DESCRIPTION).
Hard wired circuitry connects the supplemental
restraint system components to each other through
the electrical system of the vehicle. These hard wired
circuits are integral to several wire harnesses, which
are routed throughout the vehicle and retained by
many different methods. These circuits may be con-
nected to each other, to the vehicle electrical system,
and to the supplemental restraint system compo-
nents through the use of a combination of soldered
splices, splice block connectors, and many different
types of wire harness terminal connectors and insu-
lators. Refer to the appropriate wiring information.
The wiring information includes wiring diagrams,
proper wire and connector repair procedures, further
details on wire harness routing and retention, as well
as pin-out and location views for the various wire
harness connectors, splices and grounds.
OPERATION
ACTIVE RESTRAINTS
The primary passenger restraints in this or any
other vehicle are the standard equipment factory-in-
stalled seat belts. Seat belts are referred to as an
active restraint because the vehicle occupants are
required to physically fasten and properly adjust
these restraints in order to benefit from them. See
the owner's manual in the vehicle glove box for more
information on the features, use and operation of all
of the factory-installed active restraints.PASSIVE RESTRAINTS
The passive restraints system is referred to as a
supplemental restraint system because they were
designed and are intended to enhance the protection
for the vehicle occupants of the vehicleonlywhen
used in conjunction with the seat belts. They are
referred to as passive systems because the vehicle
occupants are not required to do anything to make
them operate; however, the vehicle occupants must
be wearing their seat belts in order to obtain the
maximum safety benefit from the factory-installed
supplemental restraint systems.
The supplemental restraint system electrical cir-
cuits are continuously monitored and controlled by a
microprocessor and software contained within the
Airbag Control Module (ACM). An airbag indicator in
the ElectroMechanical Instrument Cluster (EMIC)
illuminates for about seven seconds as a bulb test
each time the ignition switch is turned to the On or
Start positions. Following the bulb test, the airbag
indicator is turned on or off by the ACM to indicate
the status of the supplemental restraint system. If
the airbag indicator comes on at any time other than
during the bulb test, it indicates that there is a prob-
lem in the supplemental restraint system electrical
circuits. Such a problem may cause airbags not to
deploy when required, or to deploy when not
required.
Deployment of the supplemental restraints
depends upon the angle and severity of an impact.
Deployment is not based upon vehicle speed; rather,
deployment is based upon the rate of deceleration as
measured by the forces of gravity (G force) upon the
impact sensors. When an impact is severe enough,
the microprocessor in the ACM signals the inflator
unit of the airbag module to deploy the airbag. Dur-
ing a frontal vehicle impact, the knee blockers work
in concert with properly fastened and adjusted seat
belts to restrain both the driver and the front seat
passenger in the proper position for an airbag deploy-
ment. The knee blockers also absorb and distribute
the crash energy from the driver and the front seat
passenger to the structure of the instrument panel.
Typically, the vehicle occupants recall more about
the events preceding and following a collision than
they have of an airbag deployment itself. This is
because the airbag deployment and deflation occur so
rapidly. In a typical 48 kilometer-per-hour (30 mile-
per-hour) barrier impact, from the moment of impact
until the airbags are fully inflated takes about 40
milliseconds. Within one to two seconds from the
moment of impact, the airbags are almost entirely
deflated. The times cited for these events are approx-
imations, which apply only to a barrier impact at the
given speed. Actual times will vary somewhat,
8O - 4 RESTRAINTSWJ
RESTRAINTS (Continued)

depending upon the vehicle speed, impact angle,
severity of the impact, and the type of collision.
When the ACM monitors a problem in any of the
airbag system circuits or components, it stores a
fault code or Diagnostic Trouble Code (DTC) in its
memory circuit and sends an electronic message to
the EMIC to turn on the airbag indicator. Proper
testing of the airbag system components, the Pro-
grammable Communication Interface (PCI) data bus,
the data bus message inputs to and outputs from the
EMIC or the ACM, as well as the retrieval or erasure
of a DTC from the ACM or EMIC requires the use of
a DRBIIItscan tool. Refer to the appropriate diag-
nostic information.
See the owner's manual in the vehicle glove box for
more information on the features, use and operation
of all of the factory-installed passive restraints.
WARNING - RESTRAINT SYSTEM
WARNING: DURING AND FOLLOWING ANY SEAT
BELT SERVICE, CAREFULLY INSPECT ALL SEAT
BELTS, BUCKLES, MOUNTING HARDWARE, AND
RETRACTORS FOR PROPER INSTALLATION,
OPERATION, OR DAMAGE. REPLACE ANY BELT
THAT IS CUT, FRAYED, OR TORN. STRAIGHTEN
ANY BELT THAT IS TWISTED. TIGHTEN ANY
LOOSE FASTENERS. REPLACE ANY BELT THAT
HAS A DAMAGED OR INOPERATIVE BUCKLE OR
RETRACTOR. REPLACE ANY BELT THAT HAS A
BENT OR DAMAGED LATCH PLATE OR ANCHOR
PLATE. NEVER ATTEMPT TO REPAIR A SEAT BELT
COMPONENT. ALWAYS REPLACE DAMAGED OR
FAULTY SEAT BELT COMPONENTS WITH THE COR-
RECT, NEW AND UNUSED REPLACEMENT PARTS
LISTED IN THE DAIMLERCHRYSLER MOPAR PARTS
CATALOG.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, FRONT IMPACT SENSOR,
SIDE IMPACT SENSOR, SIDE CURTAIN AIRBAG, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. DISCONNECT AND ISOLATE THE BAT-
TERY NEGATIVE (GROUND) CABLE, THEN WAIT
TWO MINUTES FOR THE SYSTEM CAPACITOR TO
DISCHARGE BEFORE PERFORMING FURTHER
DIAGNOSIS OR SERVICE. THIS IS THE ONLY SURE
WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.WARNING: AN AIRBAG INFLATOR UNIT MAY CON-
TAIN SODIUM AZIDE AND POTASSIUM NITRATE.
THESE MATERIALS ARE POISONOUS AND
EXTREMELY FLAMMABLE. CONTACT WITH ACID,
WATER, OR HEAVY METALS MAY PRODUCE HARM-
FUL AND IRRITATING GASES (SODIUM HYDROXIDE
IS FORMED IN THE PRESENCE OF MOISTURE) OR
COMBUSTIBLE COMPOUNDS. AN AIRBAG INFLA-
TOR UNIT MAY ALSO CONTAIN A GAS CANISTER
PRESSURIZED TO OVER 2500 PSI. DO NOT
ATTEMPT TO DISMANTLE AN AIRBAG UNIT OR
TAMPER WITH ITS INFLATOR. DO NOT PUNCTURE,
INCINERATE, OR BRING INTO CONTACT WITH
ELECTRICITY. DO NOT STORE AT TEMPERATURES
EXCEEDING 93É C (200É F).
WARNING: REPLACE ALL RESTRAINT SYSTEM
COMPONENTS ONLY WITH PARTS SPECIFIED IN
THE DAIMLERCHRYSLER MOPAR PARTS CATA-
LOG. SUBSTITUTE PARTS MAY APPEAR INTER-
CHANGEABLE, BUT INTERNAL DIFFERENCES MAY
RESULT IN INFERIOR OCCUPANT PROTECTION.
WARNING: THE FASTENERS, SCREWS, AND
BOLTS ORIGINALLY USED FOR THE RESTRAINT
SYSTEM COMPONENTS HAVE SPECIAL COATINGS
AND ARE SPECIFICALLY DESIGNED FOR THE
RESTRAINT SYSTEM. THEY MUST NEVER BE
REPLACED WITH ANY SUBSTITUTES. ANY TIME A
NEW FASTENER IS NEEDED, REPLACE IT WITH
THE CORRECT FASTENERS PROVIDED IN THE
SERVICE PACKAGE OR SPECIFIED IN THE
DAIMLERCHRYSLER MOPAR PARTS CATALOG.
WARNING: WHEN A STEERING COLUMN HAS AN
AIRBAG UNIT ATTACHED, NEVER PLACE THE COL-
UMN ON THE FLOOR OR ANY OTHER SURFACE
WITH THE STEERING WHEEL OR AIRBAG UNIT
FACE DOWN.
DIAGNOSIS AND TESTING - SUPPLEMENTAL
RESTRAINT SYSTEM
Proper diagnosis and testing of the supplemental
restraint system components, the PCI data bus, the
data bus message inputs to and outputs from the
ElectroMechanical Instrument Cluster (EMIC) or the
Airbag Control Module (ACM), as well as the
retrieval or erasure of a Diagnostic Trouble Code
(DTC) from the ACM requires the use of a DRBIIIt
scan tool. Refer to the appropriate diagnostic infor-
mation.
WJRESTRAINTS 8O - 5
RESTRAINTS (Continued)

(4) Check to be certain that nobody is in the vehi-
cle, then reconnect the battery negative cable.
(5) Using the DRBIIIt, read and record the active
(current) Diagnostic Trouble Code (DTC) data.
(6) Next, use the DRBIIItto read and record any
stored (historical) DTC data.
(7) If any DTC is found in Step 5 or Step 6, refer
to the appropriate diagnostic information.
(8) Use the DRBIIItto erase the stored DTC data.
If any problems remain, the stored DTC data will not
erase. Refer to the appropriate diagnostic informa-
tion to diagnose any stored DTC that will not erase.
If the stored DTC information is successfully erased,
go to Step 9.
(9) Turn the ignition switch to the Off position for
about fifteen seconds, and then back to the On posi-
tion. Observe the airbag indicator in the instrument
cluster. It should light for six to eight seconds, and
then go out. This indicates that the supplemental
restraint system is functioning normally and that the
repairs are complete. If the airbag indicator fails to
light, or lights and stays on, there is still an active
supplemental restraint system fault or malfunction.
Refer to the appropriate diagnostic information to
diagnose the problem.
AIRBAG CONTROL MODULE
DESCRIPTION
The Airbag Control Module (ACM) is also some-
times referred to as the Occupant Restraint Control-
ler (ORC) (Fig. 6). The ACM is concealed underneath
the center floor console, where it is secured by four
screws to a stamped steel mounting bracket welded
onto the top of the floor panel transmission tunnel
just forward of the park brake mechanism in the pas-
senger compartment of the vehicle.
Concealed within a hollow in the center of the die
cast aluminum ACM housing is the electronic cir-
cuitry of the ACM which includes a microprocessor,
an electronic impact sensor, an electronic safing sen-
sor, and an energy storage capacitor. A stamped
metal cover plate is secured to the bottom of the
ACM housing with four screws to enclose and protect
the internal electronic circuitry and components. A
printed label on the top of the ACM housing provides
a visual verification of the proper orientation of the
unit, and should always be pointed toward the front
of the vehicle.
Two molded plastic electrical connector receptacles
exit the forward side of the ACM housing. These two
receptacles connect the ACM to the vehicle electrical
system through a dedicated take out and connector of
the instrument panel wire harness, and a dedicated
take out and connector of the airbag overlay wire
harness. For vehicles equipped with the optional side
curtain airbags, both ACM connector receptacles are
black in color and the ACM contains a second bi-di-
rectional safing sensor for the side airbags. For vehi-
cles not equipped with the optional side curtain
airbags, the ACM connector receptacles are both
gray.
The impact sensor and safing sensor internal to
the ACM are calibrated for the specific vehicle, and
are only serviced as a unit with the ACM. The ACM
cannot be repaired or adjusted and, if damaged or
faulty, it must be replaced.
OPERATION
The microprocessor in the Airbag Control Module
(ACM) contains the supplemental restraint system
logic circuits and controls all of the 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 DRBIIItscan tool using the Programma-
ble Communications Interface (PCI) data bus net-
work. This method of communication is used for
control of the airbag indicator in the ElectroMechani-
cal 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/ELECTRONIC CONTROL MOD-
ULES/COMMUNICATION - OPERATION).
Fig. 6 Airbag Control Module
1 - AIRBAG CONTROL MODULE
2 - ORIENTATION ARROW
3 - LABEL
4 - MOUNTING HOLES (4)
5 - CONNECTOR RECEPTACLE (2)
WJRESTRAINTS 8O - 9
RESTRAINTS (Continued)

The ACM microprocessor continuously monitors all
of the supplemental restraint system electrical cir-
cuits 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 for-
ever.
The ACM receives battery current through two cir-
cuits, on a fused ignition switch output (run) circuit
through a fuse in the Junction Block (JB), and on a
fused ignition switch output (start-run) circuit
through a second fuse in the JB. The ACM is
grounded through a ground circuit and take out of
the instrument panel floor wire harness. This take
out has a single eyelet terminal connector secured by
a nut to a ground stud located behind the ACM
mount on the floor panel transmission tunnel. These
connections allow the ACM to be operational when-
ever the ignition switch is in the Start or On posi-
tions. 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
airbags for up to one second following a battery dis-
connect or failure. The purpose of the capacitor is to
provide backup supplemental restraint system pro-
tection in case there is a loss of battery current sup-
ply 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 brackets on the inboard
sides 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 provide
verification of the direction and severity of an
impact. On models equipped with optional side cur-
tain airbags, the ACM also monitors inputs from two
remote side impact sensors located near the base of
both the left and right inner B-pillars to control the
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 safingsensor is used to verify the need for an airbag
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. The ACM also monitors a
Hall effect-type seat belt switch located in the buckle
of each front seat belt to determine whether the seat-
belts are buckled, and provides an input to the EMIC
over the PCI data bus to control the seatbelt indica-
tor operation based upon the status of the driver side
front seat belt switch. Vehicles with the optional side
curtain airbags feature a second safing sensor within
the ACM to provide confirmation to the ACM of side
impact forces. This second safing sensor is a bi-direc-
tional 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.
The ACM also determines the level of front airbag
deployment force required for each front seating posi-
tion based upon the status of the two seat belt switch
inputs and the severity of the monitored impact.
When the programmed conditions are met, the ACM
sends the proper electrical signals to deploy the mul-
tistage dual front airbags at the programmed force
levels, and to deploy either side curtain airbag.
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 net-
work, and the electronic message inputs to and out-
puts from the ACM requires the use of a DRBIIIt
scan tool. Refer to the appropriate diagnostic infor-
mation.
REMOVAL
Two different Airbag Control Modules (ACM) are
available for this vehicle. For vehicles equipped with
the optional side curtain airbags, both ACM connec-
tor receptacles are black in color and the ACM con-
tains a second bi-directional safing sensor for the
side airbags. For vehicles not equipped with the
optional side curtain airbags, the ACM connector
receptacles are gray.
8O - 10 RESTRAINTSWJ
AIRBAG CONTROL MODULE (Continued)

OPERATION
The front impact sensors are electronic accelerom-
eters that sense the rate of vehicle deceleration,
which provides verification of the direction and sever-
ity of an impact. Each sensor also contains an elec-
tronic 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 con-
tinuously monitors all of the 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 conven-
tional diagnostic tools and procedures. However, con-
ventional 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. Refer to the appropriate diagnostic infor-
mation.
REMOVAL
The front and side impact sensors are interchange-
able except that the front impact sensors are serviced
with a right or left mounting bracket, while the side
impact sensors use no mounting bracket. If a front
impact sensor is faulty, but not damaged, the sensor
may be removed from the sensor mounting bracket
and replaced with a side impact sensor. If the front
impact sensor or the sensor mounting bracket are
damaged in any way, or if proper tightening torque of
the screws that secure the sensor to the bracket can-
not be achieved, the front impact sensor and bracket
must be replaced as a unit.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, FRONT IMPACT SENSOR,
SIDE IMPACT SENSOR, SIDE CURTAIN AIRBAG, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. DISCONNECT AND ISOLATE THE BAT-
TERY NEGATIVE (GROUND) CABLE, THEN WAIT
TWO MINUTES FOR THE SYSTEM CAPACITOR TO
DISCHARGE BEFORE PERFORMING FURTHERDIAGNOSIS OR SERVICE. THIS IS THE ONLY SURE
WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
WARNING: THE FRONT IMPACT SENSOR ENABLES
THE SYSTEM TO DEPLOY THE FRONT SUPPLE-
MENTAL RESTRAINTS. NEVER STRIKE OR DROP
THE FRONT IMPACT SENSOR, AS IT CAN DAMAGE
THE IMPACT SENSOR OR AFFECT ITS CALIBRA-
TION. IF AN IMPACT SENSOR IS ACCIDENTALLY
DROPPED DURING SERVICE, THE SENSOR MUST
BE SCRAPPED AND REPLACED WITH A NEW UNIT.
FAILURE TO OBSERVE THIS WARNING COULD
RESULT IN ACCIDENTAL, INCOMPLETE, OR
IMPROPER FRONT SUPPLEMENTAL RESTRAINT
DEPLOYMENT AND POSSIBLE OCCUPANT INJU-
RIES.
(1) Disconnect and isolate the battery negative
cable. Wait two minutes for the system capacitor to
discharge before further service.
(2) From the engine compartment, disconnect the
right or left headlamp and dash wire harness connec-
tor for the front impact sensor from the sensor con-
nector receptacle (Fig. 25).
Fig. 25 Front Impact Sensor Remove/Install (Right
Side Shown, Left Side Similar)
1 - BRACKET
2 - IMPACT SENSOR
3 - RADIATOR SUPPORT
4 - WIRE HARNESS CONNECTOR
5 - SCREW (2)
8O - 24 RESTRAINTSWJ
FRONT IMPACT SENSOR (Continued)