Headlamp High Beam Indicator Lamp; Low Fuel Warning Lamp; Malfunction Indicator Lamp; Master Lighting Indicator Lamp - Jeep 1997 Grand Cherokee Service Manual

8E - 8 INSTRUMENT PANEL SYSTEMS
DESCRIPTION AND OPERATION (Continued)
Vehicles equipped with the automatic headlamps
option have an automatic funeral mode or parade
mode. In this mode, the BCM uses an input from the
automatic headlamp light sensor to determine the
ambient light levels. If the BCM decides that the
exterior lighting is turned on in the daylight, it over-
rides the selected panel dimmer switch signal by
sending a message on the CCD bus to illuminate all
vacuum fluorescent displays at full brightness for
easier visibility in daytime light levels. The auto-
matic funeral mode or parade mode has no effect on
the incandescent bulb dimming levels.
Refer to Group 8L - Lamps for more information.
CRUISE-ON INDICATOR LAMP
The cruise-on indicator lamp gives an indication
when the vehicle speed control system is turned on,
even when the system is not currently engaged. The
lamp is turned on by the instrument 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 Powertrain Control Module (PCM) on the
Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the analog resistor-
multiplexed vehicle speed control switches in the
steering wheel to decide whether to turn the lamp on
or off. The PCM then sends the proper message to
the instrument cluster on the CCD data bus. Refer to
Group 8H - Vehicle Speed Control System for more
information.

HEADLAMP HIGH BEAM INDICATOR LAMP

The headlamp high beam indicator lamp gives an
indication when the headlamp high beams are turned
on. The lamp is turned on by the instrument 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 an input from the headlamp dim-
mer (multi-function) switch to decide whether the
headlamp high beams are turned on. It then sends
the proper message to the instrument cluster on the
CCD data bus to turn the lamp on or off. Refer to
Group 8L - Lamps for more information.

LOW FUEL WARNING LAMP

The low fuel warning lamp gives an indication
when the fuel level in the fuel tank has fallen below
about one-eighth of a full tank, as registered on the
fuel gauge. The instrument cluster circuitry lights
the lamp for about four seconds when the ignition
switch is turned to the On position as a bulb test.
After the bulb test, the instrument cluster circuitry
controls the lamp based upon a message received
from the Body Control Module (BCM) on the
Chrysler Collision Detection (CCD) data bus.
The BCM uses a fuel level message received from
the Powertrain Control Module (PCM) on the CCD
data bus to decide when the fuel level is low. The
BCM then sends the proper message to the instru-
ment cluster on the CCD data bus to turn the lamp
on or off. When the lamp-on message is sent, the
BCM also issues a single low fuel warning chime
tone. Once the lamp is turned on, an increase in the
fuel level of at least one-half gallon is required before
the PCM input to the BCM will change and cause a
lamp-off message to be issued. If the PCM detects a
short or open in the fuel gauge sending unit circuit,
it sends a message on the CCD data bus that will
cause the fuel gauge pointer to move to the empty
stop and the low fuel lamp to be turned on.

MALFUNCTION INDICATOR LAMP

The Check Engine or Malfunction Indicator Lamp
(MIL) gives an indication when the Powertrain Con-
trol Module (PCM) has recorded a Diagnostic Trouble
Code (DTC) for an On-Board Diagnostics II (OBDII)
emissions-related circuit or component malfunction.
The lamp is turned on by the instrument cluster cir-
cuitry for about three 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 PCM on the Chrysler Collision
Detection (CCD) data bus.
The PCM uses inputs from many emissions-related
circuits and sensors, along with its internal program-
ming, to decide whether a condition exists that
requires the MIL lamp to be turned on. The PCM
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
MIL lamp-on message from the PCM, it sends a
chime request message to the Body Control Module
(BCM) on the CCD data bus for a single chime tone
to sound.
The MIL lamp can also be used to display a stored
DTC by flashing on and off. Refer to Group 14 - Fuel
Systems for more information on the PCM or the
PCM inputs. Refer to Group 25 - Emission Control
Systems for more information on DTCs and their
retrieval.

MASTER LIGHTING INDICATOR LAMP

Vehicles sold in countries where it is required
equipment, have a master lighting indicator lamp.
The master lighting indicator lamp gives an indica-
ZG