When the Overdrive mode is engaged, the transmission automatically upshifts to second, third and fourth (overdrive) gears. If the Overdrive mode switch is disengaged, the transmission will not upshift to fourth (overdrive). Under normal driving conditions, the selector should be in the D position and the Overdrive mode switch should be engaged.
If you need to pick up speed quickly, fully depress the gas pedal. The transmission will automatically downshift depending on the speed and engine load.