Anti-Lock Brake System Lamp; Brake Warning Lamp; Check Gauges Lamp; Cluster Illumination Lamp - Jeep 1997 Grand Cherokee Service Manual

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DESCRIPTION AND OPERATION (Continued)
The airbag indicator lamp also has a lamp backup
feature. Following the seat belt reminder lamp dis-
play function, if an inoperative airbag warning lamp
circuit was detected during the bulb test sequence,
the instrument cluster circuitry will flash the seat
belt reminder lamp on and off for about twenty sec-
onds. If the seat belt reminder lamp flashes longer
than twenty seconds, or flashes at any time other
than about twenty seconds after the initial igni-
tion-on sequence, it indicates an airbag system fault
has been detected and that the airbag indicator lamp
is inoperative.
Refer to Group 8M - Passive Restraint Systems for
more information on the airbag system.

ANTI-LOCK BRAKE SYSTEM LAMP

The Anti-Lock Brake System (ABS) lamp gives an
indication when the ABS system is faulty or inoper-
ative. The lamp is hard-wired in the instrument clus-
ter, and is completely controlled by the Controller
Anti-lock Brake (CAB). It receives battery voltage
through the instrument cluster fused ignition switch
output feed circuit, and is grounded by the CAB. The
lamp is turned on by the CAB for about two seconds
when the ignition switch is turned to the On position
as a bulb test. After the bulb test, the CAB turns the
lamp on or off based upon the results of the ABS sys-
tem self-tests.
The CAB continually monitors the ABS circuits
and sensors to decide whether the system is in good
operating condition. If the CAB turns the lamp on
after the bulb test, it indicates that the CAB has
detected a system malfunction and/or that the ABS
system has become inoperative. Refer to Group 5 -
Brakes for more information.

BRAKE WARNING LAMP

The brake warning lamp gives an indication when
the parking brake is applied, or when the pressures
in the two halves of the split brake hydraulic system
are unequal. The lamp is turned on by the instru-
ment cluster circuitry for about four seconds when
the ignition switch is turned to the On position as a
bulb test. After the bulb test, the lamp is controlled
by the instrument cluster circuitry based upon a
message received from the Body Control Module
(BCM) on the Chrysler Collision Detection (CCD)
data bus.
The BCM uses inputs from the parking brake
switch and the brake warning switch to decide
whether the brake warning lamp should be on or off.
The BCM then sends the proper message to the
instrument cluster on the CCD data bus to turn the
lamp on or off.
The brake warning switch closes to ground when it
senses unequal hydraulic pressures in the two halves
INSTRUMENT PANEL SYSTEMS
of the split brake hydraulic system, possibly due to
low brake fluid level or brake fluid leakage. The
parking brake switch closes to ground when the
parking brake is applied. Refer to Group 5 - Brakes
for more information.

CHECK GAUGES LAMP

The check gauges lamp gives an indication when
certain gauges reflect a condition requiring immedi-
ate attention. The lamp is turned on by the instru-
ment cluster circuitry for about three seconds after
the ignition switch is turned to the On position as a
bulb test. After the bulb test, the lamp is controlled
by the instrument cluster circuitry based upon a
message received from either the Body Control Mod-
ule (BCM) or the Powertrain Control Module (PCM)
on the Chrysler Collision Detection (CCD) data bus.
The BCM and PCM use several inputs to decide
whether a condition exists requiring the check
gauges lamp to be turned on. The responsible module
then sends the proper message to the instrument
cluster on the CCD data bus to turn the lamp on or
off. When the instrument cluster circuitry receives a
check gauges lamp-on message, it sends a chime
request message to the BCM on the CCD data bus
for a chime tone to sound.
The conditions monitored and the responsible mod-
ules are:
• Engine coolant temperature is high or critical
(BCM)
• Engine oil pressure is low (BCM)
• Charging system failure (PCM)
• System voltage is high (PCM).

CLUSTER ILLUMINATION LAMP

When the park or head lamps are on, the cluster
illumination lamps light. Illumination brightness is
adjusted by sliding the panel dimmer switch knob
(downwards to dim, upwards to brighten). Each of
the instrument cluster illumination lamps receives
pulse-width modulated battery feed from the Body
Control Module (BCM) on the hard-wired panel
lamps driver circuit. The BCM monitors the panel
dimmer resistor switch to determine the desired dim-
ming level, then adjusts the pulse-width signal
accordingly.
The BCM also sends the proper panel lamps dim-
ming level message on the Chrysler Collision Detec-
tion (CCD) data bus to control the dimming levels of
the various vacuum fluorescent displays. All modules
on the CCD data bus with vacuum fluorescent dis-
plays (instrument cluster, radio, mini trip computer,
vehicle information center) receive this message and
adjust their dimming levels to match that of the
incandescent cluster
directly by the BCM.
illumination bulbs
8E - 7
driven