Shift Indicator - A/T: Description and Operation
SHIFT INDICATOR (TRANSFER CASE)DESCRIPTION
4WD LOW INDICATOR
A 4WD low indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional four-wheel drive system and electronically shifted transfer case, this indicator is electronically disabled. This indicator is located near the bottom of the cluster overlay, between the speedometer and the tachometer. Illumination of this indicator may also be accompanied by the display of certain textual messages in the cluster dot matrix display.
The 4WD low indicator consists of a stencil-like cutout of the text 4WD LOW in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. An amber Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the indicator to appear in amber through the translucent outer layer of the overlay when it is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board.
When the exterior lighting is turned ON, the illumination intensity of the tow/haul indicator is dimmable, which is adjusted along with the cluster illumination lighting using the panel lamps dimmer control sleeve on the left multifunction switch control stalk.
The 4WD indicator is serviced as a unit with the instrument cluster.
4WD NEUTRAL INDICATOR
A 4WD neutral indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional four-wheel drive system and electronically shifted transfer case, this indicator is electronically disabled. However, on vehicles not equipped with the optional four-wheel drive system and electronically shifted transfer case, this indicator is electronically disabled. The 4WD neutral indication appears within the reconfigurable dot matrix Organic Light Emitting Diode (OLED) display unit. The 4WD neutral indicator consists of a textual 4WD SYSTEM IN NEUTRAL message which appears in place of the compass/trip computer information in the dot matrix display.
The dot matrix OLED is soldered onto the 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 OLED prevents it from being clearly visible when it is not illuminated. The 4WD neutral indicator textual message appears in the same blue-green color and at the same lighting level as the compass/trip computer information when they are illuminated by the instrument cluster electronic circuit board.
The 4WD neutral indicator is serviced as a unit with the OLED in the instrument cluster.
OPERATION
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:
- 4WD Low Lamp-On Message - Each time the cluster receives a 4WD low 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 4WD low lamp-off message from the FDCM, or until the ignition switch is turned to the OFF position, whichever occurs first.
- 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 electronic messages 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 instrument cluster dot matrix display to accompany a flashing 4WD low indicator.
- 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 messages to the instrument cluster. For proper diagnosis of the transfer case shift motor/mode sensor, the FDCM, the CAN data bus, or the electronic message inputs to the instrument cluster that control the 4WD low indicator, a diagnostic scan tool is required.
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 a 4WD neutral lamp-on message from the FDCM, the indicator will be illuminated. The indicator remains illuminated until the cluster receives a 4WD neutral lamp-off message from the FDCM 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 messages to the instrument cluster. For proper diagnosis of the transfer case shift motor/mode sensor, the FDCM, the CAN data bus, or the electronic message inputs to the instrument cluster that control the 4WD neutral indicator, a diagnostic scan tool is required.