Grand Cherokee 4WD V8-4.7L (2003)
Cruise Control Indicator Lamp: Description and Operation
CRUISE INDICATOR
A cruise indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional speed control system, this
indicator is electronically disabled. The cruise indicator is located on the right edge of the instrument cluster, to the right of the speedometer. The
cruise indicator consists of the word "CRUISE" imprinted on a blue/green lens. The lens is located behind a cutout 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. The
"CRUISE" text appears silhouetted against a blue/green field through the translucent outer layer of the overlay when the indicator is illuminated from
behind by a replaceable bulb and bulb holder unit located on the instrument cluster electronic circuit board. When the exterior lighting is turned On,
the illumination intensity of the cruise indicator is dimmable, which is adjusted along with the cluster illumination lighting using the panel lamps
dimmer control ring on the control stalk of the left multi-function switch. The cruise indicator lens is serviced as a unit with the instrument cluster lens,
hood and mask unit.
The cruise indicator gives an indication to the vehicle operator when the speed control system is turned On, regardless of whether the speed control is
engaged. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages
received by the cluster from the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus. The cruise
indicator bulb 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) circuit. Therefore, the bulb will always be off
when the ignition switch is in any position except On or Start. The bulb only illuminates when it is provided a path to ground by the instrument cluster
transistor. The instrument cluster will turn on the cruise indicator for the following reasons:
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Cruise Lamp-On Message - Each time the cluster receives a cruise lamp-on message from the PCM indicating the speed control system has been
turned On, the cruise indicator is illuminated. The indicator remains illuminated until the cluster receives a cruise lamp-off message from the PCM
or until the ignition switch is turned to the Off position, whichever occurs first.
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Actuator Test - Each time the cluster is put through the actuator test, the cruise indicator will be turned on for the duration of the test to confirm
the functionality of the bulb and the cluster control circuitry
The PCM continually monitors the speed control switches to determine the proper outputs to the speed control servo. The PCM then sends the proper
cruise indicator lamp-on and lamp-off messages to the instrument cluster. If the cruise indicator fails to light during the actuator test, replace the bulb
with a known good unit. For further diagnosis of the cruise indicator or the instrument cluster circuitry that controls the indicator, refer to Instrument
Cluster Diagnosis and Testing. For proper diagnosis of the speed control switches, the PCM, the PCI data bus, or the electronic message inputs to the
instrument cluster that control the cruise indicator, a DRBIII scan tool is required Refer to the appropriate diagnostic information.
