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TJ
AIRBAG INDICATOR (Continued)
remains illuminated for about twelve seconds or until
the cluster receives a single lamp-off message from
the ACM, whichever is longer.
• Actuator Test - Each time the cluster is put
through the actuator test, the airbag indicator will be
turned on, then off again during the bulb check por-
tion of the test to confirm the functionality of the
LED and the cluster control circuitry.
The ACM continually monitors the airbag system
circuits and sensors to decide whether the system is
in good operating condition. The ACM then sends the
proper lamp-on or lamp-off messages to the instru-
ment cluster. If the ACM sends a lamp-on message
after the bulb test, it indicates that the ACM has
detected a system malfunction and/or that the air-
bags may not deploy when required, or may deploy
when not required. The ACM will store a Diagnostic
Trouble Code (DTC) for any malfunction it detects.
Each time the airbag indicator fails to illuminate due
to an open or short in the cluster airbag indicator cir-
cuit, the cluster sends a message notifying the ACM
of the condition and stores a DTC. For further diag-
nosis of the airbag indicator or the instrument clus-
ter circuitry that controls the indicator, (Refer to 8 -
ELECTRICAL/INSTRUMENT CLUSTER - DIAGNO-
SIS AND TESTING). For proper diagnosis of the air-
bag system, the ACM, the PCI data bus, or the
message inputs to the instrument cluster that control
the airbag indicator, a DRBIII scan tool is required.
Refer to the appropriate diagnostic information.
BRAKE/PARK BRAKE
INDICATOR
DESCRIPTION
A brake indicator is standard equipment on all
instrument clusters. The brake indicator is located
near the lower edge of the instrument cluster overlay,
to the left of the odometer/trip odometer Vacuum-Flu-
orescent Display (VFD). The brake indicator consists
of a stencil-like cutout of the word "BRAKE" in the
opaque layer of the instrument cluster overlay. The
dark outer layer of the overlay prevents the indicator
from being clearly visible when it is not illuminated.
A red lens behind the cutout in the opaque layer of
the overlay causes the "BRAKE" text to appear in
red through the translucent outer layer of the over-
lay when the indicator is illuminated from behind by
a Light Emitting Diode (LED) soldered onto the
instrument cluster electronic circuit board. The brake
indicator is serviced as a unit with the instrument
cluster.
2001 JEEP WRANGLER
OPERATION
The brake indicator gives an indication to the vehi-
cle operator when the parking brake is applied, or
when there are certain brake hydraulic system mal-
functions. This indicator is controlled by a transistor
on the instrument cluster electronic circuit board
based upon cluster programming, electronic messages
received by the cluster from the Powertrain Control
Module (PCM) over the Programmable Communica-
tions Interface (PCI) data bus, and hard wired inputs
to the instrument cluster from the park brake switch
and the brake warning indicator switch. The brake
indicator Light Emitting Diode (LED) receives bat-
tery current on the instrument cluster electronic cir-
cuit board through the fused ignition switch output
(run-start) circuit whenever the ignition switch is in
the On or Start positions; therefore, the LED will
always be off when the ignition switch is in any posi-
tion except On or Start. The LED only illuminates
when it is provided a path to ground by the instru-
ment cluster transistor. The instrument cluster will
turn on the brake indicator for the following reasons:
• Bulb Test - Each time the ignition switch is
turned to the On or Start positions the brake indica-
tor is illuminated for about four seconds as a bulb
test.
• Park Brake Switch Input - Each time the
cluster detects ground on the red brake warning indi-
cator driver circuit (park brake switch closed = park
brake applied or not fully released) the brake indica-
tor is illuminated solid. If a vehicle speed message is
received by the cluster from the PCM over the PCI
data bus indicating the vehicle is moving while the
red brake warning indicator driver input is ground,
the brake indicator is flashed on and off repeatedly.
Whether illuminated solid or flashing, the indicator
remains illuminated until the red brake warning
indicator driver input to the cluster is an open circuit
(park brake switch open = park brake fully released),
or until the ignition switch is turned to the Off posi-
tion, whichever occurs first.
• Brake Hydraulic System Malfunction - Each
time the cluster detects ground on the red brake
warning indicator driver circuit (brake warning indi-
cator switch closed = pressures in the two halves of
the split brake hydraulic system are unequal) the
brake indicator is illuminated solid. The indicator
remains illuminated until the red brake warning
indicator driver input to the cluster is an open circuit
(brake warning indicator switch open = brake
hydraulic system pressures are equal), or until the
ignition switch is turned to the Off position, which-
ever occurs first.
• Actuator Test - Each time the instrument clus-
ter is put through the actuator test, the brake indi-
cator will be turned on, then off again during the
INSTRUMENT CLUSTER
8Js - 17
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