Overdrive Switch: Description and Operation

The Transmission Control Switch (TCS) is a momentary contact switch. When the switch is pressed, a signal is sent to the Powertrain Control Module (PCM) to allow automatic shifts from first through fourth gears or first through third gears only. The PCM energizes the Transmission Control Indicator Lamp (TCIL) when the switch has been pressed to cancel overdrive. The TCIL indicates overdrive cancel mode activated (lamp ON) and Electronic Pressure Control (EPC) circuit shorted (lamp flashing) or monitored sensor failure.