Overdrive Indicator Lamp: Description and Operation

^ The Transmission Control Switch (TCS) is a momentary contact switch. When this switch is pressed, a signal is sent to the Powertrain Control Module (PCM).
^ The powertrain control module then energizes the Transmission Control Indicator Lamp (TCIL) and toggles Solenoid 3 (SS3), applying the forward clutch to provide engine braking and canceling fourth gear operation.