OVERDRIVE OFF INDICATOR
DESCRIPTION
An overdrive off indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional overdrive automatic transmission, this indicator is electronically disabled. This indicator is located above the fuel gauge and to the left of the speedometer in the cluster overlay.
The overdrive off indicator consists of a stencil-like cutout of the text O/D OFF 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 overdrive off indicator is dimmable, which is adjusted along with the cluster illumination lighting using the panel lamps dimmer control ring on the left control stalk of the multi-function switch.
The overdrive off indicator is serviced as a unit with the instrument cluster.
OPERATION
The overdrive off indicator gives an indication to the vehicle operator when the Off position of the overdrive off switch has been selected, disabling the electronically controlled overdrive feature of the automatic transmission. 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 Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus.
The overdrive off 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 overdrive off indicator for the following reasons:
- Overdrive Off Indicator Lamp-On Message - Each time the cluster receives an electronic overdrive off indicator lamp-ON message from the PCM the overdrive off indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the PCM, 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 overdrive off indicator will be turned ON, then OFF again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.
The PCM continually monitors the overdrive off switch to determine the appropriate outputs to the automatic transmission. The PCM then sends the proper lamp-ON and lamp-OFF messages to the ElectroMechanical Instrument Cluster (EMIC).
For proper diagnosis of the overdrive control system, the PCM, the EMIC, the PCI data bus or the electronic communication related to overdrive off indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.