OPERATION
PART TIME INDICATOR
The part time indicator gives an indication to the vehicle operator whenever a part time operating mode of the four-
wheel drive transfer case is selected. On vehicles equipped with the Command-Trac four-wheel drive system, the
part time indicator lights when the transfer case is engaged in the “4H” or “4L” positions. On vehicles equipped with
the Selec-Trac four-wheel drive system, the part time indicator lights when the transfer case is engaged in the “4 X
4 Part Time” position. 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 instrument cluster must be electronically configured for the type of transfer case in the vehicle using a diag-
nostic scan tool in order to provide proper operation of the part time indicator. The part time 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 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 part time indicator for the following reasons:
•
Part Time Lamp-On Message - Each time the cluster receives a part time lamp-on message from the PCM
indicating that a part time position of the four-wheel drive transfer case has been selected, the part time indi-
cator will be illuminated. The indicator remains illuminated until the cluster receives a part time lamp-off mes-
sage from the PCM or until the ignition switch is turned to the Off position, whichever occurs first.
•
Actuator Test - Each time the cluster is put through the actuator test, the part time indicator will be turned on,
then off again during the bulb check portion of the test to confirm the functionality of the LED and the cluster
control circuitry.
The PCM continually monitors the transfer case switch to determine the driveline operating mode. The PCM then
sends the proper part time lamp-on and lamp-off messages to the instrument cluster. For further diagnosis of the
part time indicator or the instrument cluster circuitry that controls the indicator, (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER - DIAGNOSIS AND TESTING).
For proper diagnosis of the transfer case switch, the PCM, the PCI data bus, or the electronic message inputs to
the instrument cluster that control the part time indicator, a diagnostic scan tool is required. Refer to the appropriate
diagnostic information.
FULL TIME INDICATOR
The full time indicator gives an indication to the vehicle operator whenever a full time operating mode of the four-
wheel drive transfer case is selected. On vehicles equipped with the Selec-Trac four-wheel drive system, the full
time indicator lights when the transfer case is engaged in the “4 X 4 Full Time” position. 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 Inter-
face (PCI) data bus.
The instrument cluster must be electronically configured for the type of transfer case in the vehicle using a diag-
nostic scan tool in order to provide proper operation of the full time indicator. The full time 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 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 full time indicator for the following reasons:
•
Full Time Lamp-On Message - Each time the cluster receives a full time lamp-on message from the PCM
indicating that a full time position of the four-wheel drive transfer case has been selected, the full time indicator
will be illuminated. The indicator remains illuminated until the cluster receives a full time lamp-off message
from the PCM or until the ignition switch is turned to the Off position, whichever occurs first.
•
Actuator Test - Each time the cluster is put through the actuator test, the full time indicator will be turned on,
then off again during the bulb check portion of the test to confirm the functionality of the LED and the cluster
control circuitry.
The PCM continually monitors the transfer case switch to determine the driveline operating mode. The PCM then
sends the proper full time lamp-on and lamp-off messages to the instrument cluster. For further diagnosis of the full
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INSTRUMENT CLUSTER
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