Transmission Mode Indicator - A/T: Description and Operation
GEAR SELECTOR INDICATORAn electronic automatic transmission gear selector indicator is standard factory-installed equipment on this model. The gear selector indicator information is displayed in a Vacuum-Fluorescent Display (VFD) unit. The VFD is part of the cluster electronic circuit board and is visible through a window with a smoked clear lens located in the lower right quadrant of the cluster overlay. The dark lens over the VFD prevents the indicator from being clearly visible when it is not illuminated. The gear selector indicator displays the following characters from left to right: "P," "R " "N "D," "2," and "1." Respectively these characters represent the park, reverse, neutral, drive, second gear, and first gear positions of the transmission gear selector lever on the steering column. The VFD illuminates a rectangular box around the character that represents the currently selected lever position.
The gear selector indicator characters and graphics appear in the same blue-green color and at the same lighting level as the odometer/trip odometer information when illuminated by the instrument cluster electronic circuit board. During daylight hours (exterior lamps OFF) the gear selector indicator VFD 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 thumbwheel on the headlamp switch. However, a "Parade" mode position of the panel lamps dimmer thumbwheel allows the VFD to be illuminated at full brightness when the vehicle is driven in daylight hours with the exterior lamps turned ON. The gear selector indicator VFD is serviced as a unit with the instrument cluster.
The electronic gear selector indicator gives an indication to the vehicle operator of the transmission gear that has been selected with the automatic transmission gear selector lever. This indicator is controlled by the instrument cluster circuit board based upon cluster programming. The cluster circuitry automatically configures itself for the proper automatic transmission model based upon a hard wired Transmission Range Sensor (TRS) input or based upon electronic messages received from the Transmission Control Module (TCM) over the Programmable Communications Interface (PCI) data bus, as the vehicle is equipped. The gear selector indicator information is displayed by a dedicated Vacuum Fluorescent Display (VFD) unit on the instrument cluster electronic circuit board, and the VFD will not display the gear selector indicator information after the ignition switch is turned to the OFF position. Each time the cluster is disconnected from battery current for more than about five minutes, it must configure itself again for the automatic transmission model that is in the vehicle when it is reconnected to battery current. The instrument cluster circuitry configures and operates the gear selector indicator VFD based upon the following inputs from the Transmission Range Sensor (TRS) or the Transmission Control Module (TCM):
- Resolved TRS Circuit/Gear Selector Indicator Message - If the transmission range sensor mux circuit is resolved, the cluster circuitry controls the gear selector indicator display based upon the resistance value of the hard wired input from the TRS. If the transmission range sensor mux circuit is not resolved, the cluster circuitry controls the gear selector indicator display based upon electronic gear selector indicator messages received from the TCM. The cluster circuitry then displays the selected gear position by illuminating a box around the proper character in the gear selector indicator (P, R, N, D, 2 or 1). The box remains illuminated around the selected gear position character until a new input value is received from the TRS on the transmission range sensor mux circuit, until another electronic gear selector indicator message is received from the TCM, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Open/Shorted TRS Circuit and No Gear Selector Indicator Message - If the transmission range sensor mux circuit is open/shorted, the cluster circuitry controls the gear selector indicator display based upon electronic messages received from the TCM over the Programmable Communications Interface (PCI) data bus. If the transmission range sensor mux circuit is open/shorted and no electronic messages are received from the TCM within three seconds, the instrument cluster circuitry will display all of the gear selector indicator position characters (P, R, N, D, 2 and 1) with no boxes to indicate the selected position until the condition is resolved 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 VFD will display all of its characters at once, then step through each character segment individually during the VFD portion of the test to confirm the functionality of the VFD and the cluster control circuitry.
On models with a TCM, the TCM continually monitors the TRS, then sends the proper electronic gear selector indicator messages to the instrument cluster. On models without a TCM, the instrument cluster continually monitors the hard wired TRS multiplexed input. For further diagnosis of the gear selector indicator or the instrument cluster circuitry that controls this function, (Refer to ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).