Transmission Control Switch (TCS)
WARNING: This page is about a different car, the 2003 Ford Windstar. However, it is still accessible from the selected car via links, so may be relevant.
The transmission control switch (TCS) is a momentary contact switch that is located in the end of the gearshift lever. A cover retains the TCS to the gearshift lever. The TCS commands the powertrain control module (PCM), through the instrument cluster using the standard corporate protocol (SCP) communication network, to disengage or engage the overdrive function of the transaxle. When overdrive (D) is disengaged, the message O/D OFF will illuminate on the instrument cluster.