FOUR-WHEEL DRIVE INDICATOR
DESCRIPTION
A four-wheel drive indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional four-wheel drive system, this indicator is electronically disabled. This indicator is located within the odometer Vacuum Fluorescent Display (VFD) unit.
The four-wheel drive indicator consists of the text 4WD in the VFD display. The odometer VFD unit is soldered onto the instrument cluster electronic circuit board, and is visible through a window with a smoked clear lens located on the lower edge of the tachometer gauge dial face of the cluster overlay. The dark lens over the VFD prevents it from being clearly visible when it is not illuminated. The four-wheel drive indicator text appears in an amber color and at the same lighting level as the odometer information when it is illuminated by the instrument cluster electronic circuit board.
During daylight hours (exterior lamps are OFF) the odometer VFD unit is illuminated at full brightness for clear visibility. At night (exterior lamps are ON), the VFD lighting level is adjusted with the other cluster illumination lamps using the panel lamps dimmer function of the interior lighting control sleeve on the left multi-function switch control stalk. However, a PARADE mode position of the control sleeve allows the VFD unit to be illuminated at full brightness if the exterior lamps are turned ON during daylight hours.
The four-wheel drive indicator is serviced as a unit with the odometer VFD unit in the instrument cluster.
OPERATION
The four-wheel drive indicator gives an indication to the vehicle operator when a four-wheel drive (4WD) mode of the transfer case is selected. This indicator is controlled by the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster over the Controller Area Network (CAN) data bus.
The four-wheel drive indicator 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 indicator only illuminates when it is energized by the instrument cluster logic circuit. The instrument cluster will turn ON the cruise indicator for the following reasons:
- Four-Wheel Drive Indicator Lamp-On Message - Each time the cluster receives an electronic four-wheel drive indicator lamp-ON message over the CAN data bus indicating that a four-wheel drive mode is selected, the four-wheel drive indicator is illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message over the CAN bus, 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 four-wheel drive indicator will be turned ON, then OFF again during the Vacuum Fluorescent Display (VFD) portion of the test in order to confirm the functionality of the VFD and the cluster control circuitry.
The ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) continually monitors messages over the CAN bus to determine when the four-wheel drive indicator should be activated or deactivated.
For proper diagnosis of the four-wheel drive switch, the EMIC, the CAN data bus or the electronic communication related to four-wheel drive indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.