Transmission Overdrive Off Switch Indicator Light

WARNING: This page is about a different car, the 2003 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

Powertrain Control Module (PCM) controls indicator light on overdrive/override switch on 46RE transmission.

An overdrive off indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the overdrive automatic transmission, this indicator is electronically disabled. The overdrive off indicator consists of the words O/D OFF, which appears in the lower portion of the electronic gear selector indicator 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 on the lower edge of the speedometer 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 O/D OFF appear in an amber color and at the same lighting level as the gear selector indicator 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 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 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 information on the overdrive off indicator or the instrument cluster circuitry that controls the indicator, see appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. 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(R) scan tool is required. For additional transmission information, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.