From the Owner Manual - UNDERSTANDING YOUR INSTRUMENT PANEL
9. Hill Descent Control Indicator Light — If Equipped
The symbol indicates the status of the Hill
Decent Control (HDC) feature. The lamp will
be on solid when HDC is armed. HDC can only
be armed when the transfer case is in the “4WD
Low” position and the vehicle speed is less then 30 mph
(48 km/h). If these conditions are not met while attempting
to use the HDC feature, the HDC indicator lamp will
From the Owner Manual - STARTING AND OPERATING
Hill Descent Control (HDC) — Four-Wheel Drive
Models With MP3023 Two-Speed Transfer Case
HDC maintains vehicle speed while descending hills
during off-road driving situations and is available in
4WD LOW range only. To enable HDC, press the HDC
switch or put the Selec-Terrain™ system in “ROCK”
mode (“ROCK” mode is only available in 4WD LOW
When HDC is enabled, the HDC icon will be illuminated
in the instrument cluster. HDC will automatically apply
the brakes to control downhill speed to the selected level
when necessary on grades greater than approximately
8%. It will usually not activate on level ground.
The HDC speed may be adjusted by the driver to suit the
driving conditions. The speed corresponds to the transmission
HDC operation can be overridden with brake application
to slow the vehicle down below the HDC control speed.
Conversely, if more speed is desired during HDC control,
the accelerator pedal will increase vehicle speed in the
usual manner. When either the brake or the accelerator is
released, HDC will control the vehicle back to the original
From the Service Manual:
HILL DESCENT INDICATOR
The hill descent indicator gives an indication to the vehicle operator when the QuadraDrive four-wheel drive transfer case gear selector is in the 4WD LOW position and the hill descent control push button in the instrument panel switch pod has been depressed to turn the feature ON. This feature uses the grade sensing logic of the CAB to sense the vehicle is descending a hill and employs the brake system to automatically control the hill descent speed of the vehicle. This indicator is controlled by the instrument cluster logic circuit based upon cluster programming and electronic messages received over the CAN data bus from the CAB.
The hill descent indicator function of the electronic 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 output (run-start) circuit. Therefore, the hill descent indication will always be OFF when the ignition switch status is anything except ON or START. The instrument cluster will turn ON the hill descent indicator for the following reasons:
Hill Descent Indicator Lamp-On Message - Each time the cluster receives an electronic hill descent indicator lamp-ON message from the CAB, the indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the CAB, until the cluster arbitrator logic determines that another display request has priority, or until the ignition switch status transitions to OFF, whichever occurs first.
The CAB continually monitors electronic message inputs from the Final Drive Control Module (FDCM) and the CCN to determine the status of the QuadraDrive four-wheel drive system and the hill descent control switch, then monitors its own internal grade sensing logic to determine when the hill descent mode should be engaged. The CAB then sends the proper lamp-ON or lamp-OFF message to the CCN.
For proper diagnosis of the hill descent control switch, the FDCM, the CAB, the CCN, the CAN data bus or the electronic communication related to hill descent indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.
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