2002 JEEP LIBERTY parking sensors

remains illuminated until the cluster receives a sin-
gle lamp-off message from the ACM.
²Actuator 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 actuator
test illumination of the airbag indicator is a function
of the instrument cluster.
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 and driver seat belt tensioner 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 circuit, the cluster
sends a message notifying the ACM of the condition,
then the instrument cluster and the ACM will each
store a DTC. For proper diagnosis of the airbag sys-
tem, the ACM, the PCI data bus, or the message
inputs to the instrument cluster that control the air-
bag indicator, a DRBIIItscan 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 tachometer dial face in the
instrument cluster. The brake indicator consists of
stencil-like cutouts of the word ªBRAKEº and the
International Control and Display Symbol icon for
ªBrake Failureº in the opaque layer of the instru-
ment cluster overlay. The dark outer layer of the
overlay prevents the indicator from being clearly vis-
ible when it is not illuminated. A red Light Emitting
Diode (LED) behind the cutout in the opaque layer of
the overlay causes the ªBRAKEº text and the icon to
appear in red through the translucent outer layer of
the overlay when the indicator is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The brake
indicator is serviced as a unit with the instrument
cluster.
OPERATION
The brake indicator gives an indication to the vehi-
cle operator when the parking brake is applied, when
there are certain brake hydraulic system malfunc-
tions as indicated by a low brake hydraulic fluid level
condition, or when the brake fluid level switch is dis-
connected. On models equipped with an optional
Antilock Brake System (ABS), the brake indicator
can also give an indication when certain faults are
detected in the ABS. 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 Controller
Antilock Brake (CAB) over the Programmable Com-
munications Interface (PCI) data bus (ABS only), and
hard wired inputs from the park brake switch and
the brake fluid level switch. The brake indicator
Light Emitting Diode (LED) is completely controlled
by the instrument cluster logic circuit, and that logic
will only allow this indicator to operate when the
instrument cluster receives a battery current input
on the fused ignition switch output (run-start) cir-
cuit. Therefore, the LED will always be off when the
ignition switch is in any position except On or Start.
The LED only illuminates when it is provided a path
to ground by the instrument cluster transistor. The
instrument cluster will turn on the brake indicator
for the following reasons:
²Bulb Test- Each time the ignition switch is
turned to the On position the brake indicator is illu-
minated by the instrument cluster for about three
seconds as a bulb test.
²Brake Lamp-On Message- Each time the
cluster receives a lamp-on message from the CAB,
the brake indicator will be illuminated. The indicator
remains illuminated until the cluster receives a
lamp-off message from the CAB, or until the ignition
switch is turned to the Off position, whichever occurs
first.
²Park Brake Switch Input- Each time the
cluster detects ground on the park brake switch
sense circuit (park brake switch closed = park brake
applied or not fully released) the brake indicator is
illuminated. The indicator remains illuminated until
the park brake switch sense 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 position, whichever occurs first.
²Brake Fluid Level Switch Input- Each time
the cluster detects ground on the red brake warning
indicator driver circuit (brake fluid level switch
closed = brake hydraulic system fluid level low) the
brake indicator is illuminated solid. The indicator
remains illuminated until the status of the red brake
warning indicator driver input to the cluster is off
(brake fluid level switch off = brake hydraulic system
KJINSTRUMENT CLUSTER 8J - 13
AIRBAG INDICATOR (Continued)

fluid level is not low), or until the ignition switch is
turned to the Off position, whichever occurs first.
²Brake Fluid Level Switch Input Fault- The
brake fluid level switch also features a 1 kilohm
diagnostic resistor connected in parallel between the
switch input and output to provide the cluster with
verification that the red brake warning indicator
driver circuit is not open. If the cluster does not see a
proper input on the red brake warning indicator
driver circuit, it will turn on the brake indicator. The
indicator remains illuminated until the red brake
warning indicator driver circuit fault is resolved, or
until the ignition switch is turned to the Off position,
whichever occurs first.
²Actuator 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
bulb check portion of the test to confirm the function-
ality of the LED and the cluster control circuitry.
The park brake switch on the park brake pedal
mechanism provides a hard wired ground input to
the instrument cluster circuitry through the park
brake switch sense circuit whenever the park brake
is applied or not fully released. The brake fluid level
switch on the brake master cylinder reservoir pro-
vides a hard wired ground input to the instrument
cluster circuitry through the red brake warning indi-
cator driver circuit whenever the fluid level in the
reservoir becomes low. On models equipped with the
optional ABS, the CAB sends the proper lamp-on or
lamp-off messages to the instrument cluster. If the
CAB sends a lamp-on message after the bulb test, it
indicates that the CAB has detected a brake hydrau-
lic system malfunction and/or that the ABS system
has become inoperative. The CAB will store a Diag-
nostic Trouble Code (DTC) for any malfunction it
detects.
For further diagnosis of the brake indicator or the
instrument cluster circuitry that controls the LED,
(Refer to 8 - ELECTRICAL/INSTRUMENT CLUS-
TER - DIAGNOSIS AND TESTING). The park brake
switch input to the instrument cluster can be diag-
nosed using conventional diagnostic tools and meth-
ods. For proper diagnosis of the brake fluid level
switch input to the instrument cluster, the antilock
brake system, the CAB, the PCI data bus, or the
electronic message inputs to the instrument cluster
that control the brake indicator, a DRBIIItscan tool
is required. Refer to the appropriate diagnostic infor-
mation.
DIAGNOSIS AND TESTING - BRAKE INDICATOR
The diagnosis found here addresses an inoperative
brake indicator condition. If there are problems with
several indicators in the instrument cluster, (Refer to
8 - ELECTRICAL/INSTRUMENT CLUSTER - DIAG-NOSIS AND TESTING). If the brake indicator stays
on with the ignition switch in the On position and
the park brake released, or comes on while driving,
(Refer to 5 - BRAKES - DIAGNOSIS AND TEST-
ING). If no brake system problem is found, the fol-
lowing procedures will help to locate a shorted or
open circuit, or a faulty park brake switch input.
Refer to the appropriate wiring information. The wir-
ing 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 connectors, splices and grounds.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SEAT BELT TENSIONER,
FRONT IMPACT SENSORS, SIDE CURTAIN AIRBAG,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-
TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER 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.
INDICATOR ILLUMINATES DURING BULB TEST, BUT DOES
NOT WHEN PARK BRAKE APPLIED
(1) Disconnect and isolate the battery negative
cable. Disconnect the front body wire harness connec-
tor for the park brake switch from the switch termi-
nal. Apply the parking brake. Check for continuity
between the park brake switch terminal and a good
ground. There should be continuity. If OK, go to Step
2. If not OK, replace the faulty park brake switch.
(2) Disconnect the instrument panel wire harness
connector for the instrument cluster from the cluster
connector receptacle. Check for continuity between
the park brake switch sense circuit cavities of the
front body wire harness connector for the park brake
switch and the instrument panel wire harness con-
nector for the instrument cluster. There should be
continuity. If not OK, repair the open park brake
switch sense circuit between the park brake switch
and the instrument cluster as required.
INDICATOR REMAINS ILLUMINATED - BRAKE SYSTEM
CHECKS OK
(1) Disconnect and isolate the battery negative
cable. Disconnect the front body wire harness connec-
8J - 14 INSTRUMENT CLUSTERKJ
BRAKE/PARK BRAKE INDICATOR (Continued)