Transmission Shift Position Indicator Lamp: 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 soldered onto 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 transmission type and 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 soldered onto 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):
- Open Circuit - If the cluster is configured for an automatic transmission and the transmission range sensor mux circuit is open, the cluster circuitry controls the gear selector indicator display based upon electronic messages received from the electronic Transmission Control Module (TCM) over the Programmable Communications Interface (PCI) data bus. If the transmission range sensor mux circuit is open and no electronic messages are received from the TCM within three seconds, the instrument cluster circuitry will not display any gear selector position until the condition is resolved or until the ignition switch is turned to the Off position, whichever occurs first.
- Resolved Circuit - 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 transmission range sensor. If the cluster is configured for an automatic transmission with a transmission range sensor input and detects a short to ground or an open in the transmission range sensor mux input, the instrument cluster circuitry will not display any gear selector position in the VFD. The VFD display for the short-to-ground and open circuit conditions will continue 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 gear selector indicator 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 transmission range sensor, then sends the proper gear selector indicator position messages to the instrument cluster. On models without a TCM, the instrument cluster continually monitors the hard wired transmission range sensor 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). For further diagnosis of the transmission range sensor on models without a TCM, (Refer to TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RE/TRANS- MISSION RANGE SENSOR - DIAGNOSIS AND TESTING) or (Refer to TRANSMISSION/ TRANSAXLE/AUTOMATIC - 46RE/TRANSMISSION RANGE SENSOR - DIAGNOSIS AND TESTING). On models with a TCM, for proper diagnosis of the transmission range sensor, the TCM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the gear selector indicator, a DRBIII(R) scan tool is required. Refer to the appropriate diagnostic information.