Transmission Control Switch (TCS)
WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. 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 located on the floor shifter knob. Pushing the transmission control switch (TCS) will either disengage or engage the overdrive function of the transmission. If the overdrive (D) is disengaged, the message O/D OFF will illuminate on the instrument panel.