Jeep 200 Cherokee, Service Manual

Page: 511 / 2119

ACM. A pre-programmed decision algorithm in the
ACM microprocessor determines when the decelera-
tion rate as signaled by the impact sensor indicates
an impact that is severe enough to require airbag
system protection. When the programmed conditions
are met, the ACM sends an electrical signal to deploy
the airbags.
In addition to the electronic impact sensor, there is
an electromechanical sensor within the ACM called a
safing sensor. The safing sensor is a normally open
series switch located in the airbag deployment circuit
of the ACM. This sensor detects impact energy of a
lesser magnitude than the electronic impact sensor,
and must be closed in order for the airbags to deploy.
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.
CLOCKSPRING
DESCRIPTION
The clockspring assembly is secured with two inte-
gral plastic latches onto the steering column lock
housing near the top of the steering column behind
the steering wheel. The clockspring is used to main-
tain a continuous electrical circuit between the fixed
clockspring wire harness on the steering column and
several electrical components that rotate with the
steering wheel. The rotating components include the
driver side airbag module, the horn switch and, if the
vehicle is so equipped, the vehicle speed control
switches.
The clockspring cannot be repaired. If the clock-
spring is faulty, damaged, or if the driver side airbag
has been deployed, the clockspring must be replaced.
OPERATION
The clockspring assembly consists of a plastic case
which contains a flat, ribbon-like, electrically conduc-
tive tape that winds and unwinds like a clockspring
with the steering wheel rotation. The electrically con-
ductive tape consists of several fine gauge copper
wire leads sandwiched between two narrow strips of
plastic film.
Like the clockspring in a timepiece, the clockspring
tape has travel limits and can be damaged by being
wound too tightly. To prevent this from occurring, the
clockspring is centered when it is installed on the
steering column. Centering the clockspring indexes
the clockspring tape to other steering components so
that it can operate within its designed travel limits.
However, if the clockspring is removed for service or
if the steering column is disconnected from the steer-
ing gear allowing the clockspring tape to change posi-
tion relative to the other steering components, it
must be re-centered following completion of the ser-
vice or it may be damaged. Refer to Clockspring
Centering in the Adjustments section of this group
for the proper centering procedures.
Service replacement clocksprings are shipped pre-
centered and with a locking pin installed. This lock-
ing pin should not be removed until the clockspring
has been installed on the steering column. If the
locking pin is removed before the clockspring is
installed on a steering column, the clockspring cen-
tering procedure must be performed.
DIAGNOSIS AND TESTING
AIRBAG SYSTEM
A DRB scan tool is required for diagnosis of the
airbag system. See the proper Diagnostic Procedures
manual for more information.
(1) 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).
(2) Turn the ignition switch to the On position.
Exit the vehicle with the DRB. Be certain that the
Fig. 1 16-Way Data Link Connector - Typical
1 – 16–WAY DATA LINK CONNECTOR
2 – BOTTOM OF INSTRUMENT PANEL
8M - 4 PASSIVE RESTRAINT SYSTEMS
XJ
DESCRIPTION AND OPERATION (Continued)