RAM 1500 Truck 2WD V8-5.7L VIN 2 (2006)
Overdrive Indicator Lamp: Description and Operation
Overdrive Off Indicator
An overdrive off indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with an optional overdrive automatic
transmission, this indicator is electronically disabled. This indicator is located on the right side of the instrument cluster, to the right of the coolant
temperature gauge.
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 text 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 thumbwheel on the headlamp switch. The overdrive off indicator is serviced as a unit with the
instrument cluster.
The overdrive off indicator gives an indication to the vehicle operator when the overdrive off feature has been selected using the tow/haul switch,
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 Controller Area Network (CAN) 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:
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Overdrive Off Lamp-On Message - Each time the cluster receives an overdrive off lamp-on message from the PCM indicating that the overdrive
off feature has been selected, the overdrive off indicator will be illuminated. The indicator remains illuminated until the cluster receives an
overdrive off lamp-off message from the PCM, or until the ignition switch is turned to the Off position, whichever occurs first.
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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 tow/haul switch to determine the proper outputs to the automatic transmission. The PCM then sends the proper
overdrive off lamp-on and lamp-off messages to the instrument cluster. For further diagnosis of the overdrive off indicator or the instrument cluster
circuitry that controls the indicator, refer to testing.
For proper diagnosis of the transmission control system, the PCM, the CAN data bus, or the electronic message inputs to the instrument cluster that
control the overdrive off indicator, a diagnostic scan tool is required.
