Airbag Control Module; Clockspring; Impact Sensor; Diagnosis And Testing - Jeep 1997 Grand Cherokee Service Manual

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DESCRIPTION AND OPERATION (Continued)
STORAGE
An airbag module must be stored in its original,
special container until used for service. Also, it must
be stored in a clean, dry environment; away from
sources of extreme heat, sparks, and high electrical
energy. Always place or store an airbag module on a
surface with its trim cover or airbag side facing up,
to minimize movement in case of an accidental
deployment.

IMPACT SENSOR

The impact sensor provides verification of the
direction and severity of an impact. One impact sen-
sor is used. It is located inside the Airbag Control
Module (ACM), which is secured to a bracket on the
floor pan transmission tunnel inside the vehicle.
The impact sensor is an accelerometer that senses
the rate of deceleration. The microprocessor in the
ACM monitors the impact sensor signal. A pre-pro-
grammed decision algorithm in the microprocessor
determines when the deceleration rate indicates an
impact that is severe enough to require airbag sys-
tem protection. When the programmed conditions are
met, the ACM sends an electrical signal to deploy the
airbag system components.
The impact sensor is calibrated for the specific
vehicle. The sensor is only serviced as a unit with the
ACM. The sensor cannot be repaired or adjusted and,
if faulty or damaged, the ACM unit must be replaced.

CLOCKSPRING

The clockspring is mounted on the steering column
behind the steering wheel. This assembly consists of
a plastic housing which contains a flat, ribbon-like,
electrically conductive tape that winds and unwinds
with the steering wheel rotation.
The clockspring is used to maintain a continuous
electrical circuit between the wire harness and the
driver side airbag module, the horn switch, the vehi-
cle speed control switches, and the remote radio
switches on vehicles that are so equipped. There are
also separate versions of the clockspring for models
equipped with or without the optional speed propor-
tional steering. Refer to Group 19 - Steering for more
information.
The clockspring must be properly centered when it
is installed on the steering column following any ser-
vice removal, or it will be damaged. See the Clock-
spring Centering procedure in this group for more
information.
The clockspring cannot be repaired. If the clock-
spring is faulty, damaged, or if the airbag has been
deployed, the clockspring must be replaced.
PASSIVE RESTRAINT SYSTEMS

AIRBAG CONTROL MODULE

The Airbag Control Module (ACM) contains the
impact sensor, and a microprocessor that monitors
the impact sensor signals and the airbag system elec-
trical circuits to determine the system readiness. The
ACM contains On-Board Diagnostics (OBD), and will
send an airbag lamp-on message to the instrument
cluster on the Chrysler Collision Detection (CCD)
data bus to light the airbag indicator lamp in the
instrument cluster when a monitored airbag system
fault occurs.
The ACM also contains an energy-storage capaci-
tor. This capacitor stores enough electrical energy to
deploy the airbags for up to one second following a
battery disconnect or failure during an impact. The
purpose of the capacitor is to provide airbag system
protection in a severe secondary impact, if the initial
impact has damaged or disconnected the battery, but
was not severe enough to deploy the airbags.
The ACM cannot be repaired and, if damaged or
faulty, it must be replaced.

DIAGNOSIS AND TESTING

AIRBAG SYSTEM

A DRB scan tool is required for diagnosis of the
airbag system. Refer to the proper Diagnostic Proce-
dures manual for more information.
(1) Disconnect and isolate the battery negative
cable. If the airbag has not been deployed, wait two
minutes for the system capacitor to discharge before
further service.
(2) Connect the DRB scan tool to the 16-way data
link wire harness connector. The connector is located
on the driver side lower edge of the instrument
panel, outboard of the steering column (Fig. 1).
(3) Turn the ignition switch to the On position.
Exit the vehicle with the DRB. Use the latest version
of the proper DRB cartridge.
(4) After checking that nobody is inside the vehi-
cle, reconnect the battery negative cable.
(5) Using the DRB, read and record the active
Diagnostic Trouble Code (DTC) data.
(6) Read and record any stored DTC data.
(7) Refer to the proper Diagnostic Procedures man-
ual, if any DTC is found in Step 5 or Step 6.
(8) Erase the stored DTC data. If any problems
remain, the stored DTC data will not erase.
(9) With the ignition switch still in the On posi-
tion, make sure nobody is in the vehicle.
(10) From outside of the vehicle (away from the
airbag modules in case of an accidental deployment)
turn the ignition switch to the Off position for about
ten seconds, and then back to the On position.
Observe the airbag indicator lamp in the instrument
cluster. It should light for six to eight seconds, and
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