RAM 3500 Truck 2WD V8-5.7L VIN D (2003)
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 the optional overdrive automatic
transmission, this indicator is electronically disabled.
The overdrive off indicator consists of the words "0/D OFF", which appear in the lower portion of the odometer/trip odometer indicator 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 on the lower edge of the tachometer gauge dial face of the cluster overlay. The dark lens over the VFD prevents the indicator from being
clearly visible when it is not illuminated. The words "0/D OFF" appear in an amber color and at the same lighting level as the odometer/trip odometer
information when they are illuminated by the instrument cluster electronic circuit board. The overdrive off indicator is serviced as a unit with the VFD
in the instrument cluster.
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 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 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 indicator will always be off when the ignition switch is in any position except On or Start. The indicator only illuminates when it
is switched to ground by the instrument cluster circuitry. 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 Off
position of the overdrive off switch 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 VFD
portion of the test to confirm the functionality of the VFD and the cluster control circuitry.
The PCM continually monitors the overdrive off 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 Instrument Cluster Diagnosis and Testing. For proper diagnosis of the overdrive control system, the PCM,
the PCI data bus, or the electronic message inputs to the instrument cluster that control the overdrive off indicator, a DRBIII scan tool is required.
Refer to the appropriate diagnostic information.
