Grand Cherokee 2WD Limited V8-4.7L (2002)
Seat Belt Reminder Lamp: Description and Operation
SEATBELT INDICATOR
A seatbelt indicator is standard equipment on all instrument clusters. The seatbelt indicator is located near the lower edge of the instrument cluster, to
the left of the tachometer. The seatbelt indicator consists of an International Control and Display Symbol icon for "Seat Belt" imprinted on a red 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 icon from
being clearly visible when the indicator is not illuminated. The icon appears silhouetted against a red field through the translucent outer layer of the
overlay when it is illuminated from behind by a Light Emitting Diode (LED), which is soldered onto the instrument cluster electronic circuit board.
The seatbelt indicator lens is serviced as a unit with the instrument cluster lens, hood and mask unit.
The seatbelt indicator gives an indication to the vehicle operator of the status of the driver side front seatbelt. This indicator is controlled by a
transistor on the instrument cluster electronic circuit board based upon cluster programming. On models equipped with airbags the indicator is also
controlled by electronic messages received by the cluster from the Airbag Control Module (ACM) over the Programmable Communications Interface
(PCI) data bus. The seatbelt 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)
circuit. Therefore, the indicator 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 seatbelt indicator for the following reasons:
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Seatbelt Reminder Function - Each time the cluster receives a battery current input on the fused ignition switch output (RUN/START) circuit,
the indicator will be illuminated as a seatbelt reminder for about six seconds, or until the ignition switch is turned to the OFF position, whichever
occurs first. This reminder function will occur regardless of the status of the electronic seat belt lamp-ON or lamp-OFF messages received by the
cluster from the ACM.
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Seat Belt Indicator lamp-ON Message - On models equipped with airbags, following the seatbelt reminder function, each time the cluster
receives a seat belt indicator lamp-ON message from the ACM indicating the driver side front seat belt is not fastened with the ignition switch in
the Start or ON positions, the seatbelt indicator will be illuminated. The indicator remains illuminated until the cluster receives a seat belt indicator
lamp-OFF message from the ACM, 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 seatbelt indicator will be turned ON for the duration of the test to
confirm the functionality of the LED and the cluster control circuitry
The instrument cluster continually monitors the status of the ignition switch through the hard wired fused ignition switch output (RUN/START) circuit
to determine when to provide the seatbelt reminder function. On models equipped with airbags, the ACM continually monitors the status of both front
seat belt switches to determine the proper airbag system response to a frontal impact of the vehicle. The ACM then sends the proper seatbelt indicator
lamp-ON and lamp-OFF messages to the instrument cluster based upon the status of the driver side front seat belt switch input. For further diagnosis
of the seatbelt indicator or the instrument cluster circuitry that controls the indicator, refer to Instrument Cluster Diagnosis and Testing. For proper
diagnosis of the seatbelt switches, the ACM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the seatbelt
indicator, a DRB III scan tool is required. Refer to the appropriate diagnostic information.
