Operation

OPERATION

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 Controller Antilock Brake (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 Controller Area Network (CAN) data bus from the CAB.

The hill descent 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 hill descent indication will always be OFF when the ignition switch is in any position 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 is turned to the OFF position, whichever occurs first.

The CAB continually monitors electronic message inputs from the Final Drive Control Module (FDCM) and the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/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 EMIC.

For proper diagnosis of the hill descent control switch, the FDCM, the CAB, the EMIC, 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.