Commander 4WD V8-4.7L (2008)
Four Wheel Drive Indicator Lamp: Description and Operation
Operation
4WD Low Indicator
4WD LOW INDICATOR
The 4WD low indicator gives an indication to the vehicle operator when the electronic transfer case has been shifted into the 4WD low mode. 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 Final Drive Control Module (FDCM) over the Controller Area Network (CAN) data bus.
The 4WD low 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 4WD low indicator for the following reasons:
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4WD Low Indicator Lamp-On Message - Each time the cluster receives an electronic 4WD low indicator lamp-ON message from the FDCM,
the indicator will be illuminated. The indicator can be flashed ON and OFF, or illuminated solid, as dictated by the FDCM message. The indicator
remains illuminated until the cluster receives a lamp-OFF message from the FDCM, or until the ignition switch is turned to the OFF position,
whichever occurs first.
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4WD Low Shift Procedure Textual Warning Messages - When the FDCM detects an attempt to shift the transfer case into or out of the 4WD
low mode using an improper shift sequence, it will send an electronic message requesting the cluster display a textual warning message. Each time
the cluster receives a textual warning request message from the FDCM, a CHECK SHIFT PROCEDURE textual message will appear within the
cluster reconfigurable dot matrix display to accompany a flashing 4WD low indicator.
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Actuator Test - Each time the cluster is put through the actuator test, the 4WD low indicator will be turned ON, then OFF again during the LED
portion of the test to confirm the functionality of the LED and the cluster control circuitry.
The FDCM continually monitors the electronic transfer case through the transfer case shift motor/mode sensor assembly to determine when the 4WD low
mode is engaged. The FDCM then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also known
as the Cab Compartment Node/CCN).
For proper diagnosis of the transfer case shift motor/mode sensor, the FDCM, the EMIC, the CAN data bus or the electronic communication related to
4WD low indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
4WD Neutral Indicator
4WD NEUTRAL INDICATOR
The 4WD neutral indicator gives an indication to the vehicle operator when the electronic transfer case has been shifted into the 4WD neutral mode. 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 Final Drive Control Module (FDCM) over the Controller Area Network (CAN) data bus.
The 4WD neutral indicator function of the reconfigurable dot matrix Organic Light Emitting Diode (OLED) display unit 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 OLED 4WD neutral indication will always be OFF when the ignition switch is in any
position except ON or START. The instrument cluster will turn ON the 4WD neutral indicator for the following reasons:
-
4WD Neutral Indicator Lamp-On Message - Each time the cluster receives an electronic 4WD neutral indicator lamp-ON message from the
FDCM, the indicator will be illuminated. The indicator remains illuminated for about five seconds, until the cluster receives a lamp-OFF message
from the FDCM, until the cluster arbitrator logic determines that another display request has priority, or until the ignition switch is turned to the
OFF position, whichever occurs first.
The FDCM continually monitors the electronic transfer case through the transfer case shift motor/mode sensor assembly to determine when the 4WD
neutral mode is engaged. The FDCM then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also
known as the Cab Compartment Node/CCN).
For proper diagnosis of the transfer case shift motor/mode sensor, the FDCM, the EMIC, the CAN data bus or the electronic communication related to
4WD neutral indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
