Ford Mystique Owner's Manual page 132

pressed, the transaxle control indicator light will illuminate
(O/D OFF) on the instrument panel. When this O/D OFF is
illuminated the transaxle will upshift and downshift from first
through third gears and provide coast braking in second and
third gears.
To return the transaxle to normal operation (first through fourth
gears) depress the TCS again. This switch may be used to cancel
overdrive any time the vehicle is being driven. Each time your
vehicle is started, the overdrive system will automatically be in
the normal overdrive mode and the light will not be
illuminated.
When to use D (Overdrive — without Transaxle Control
Switch Activated)
D (Overdrive) is the usual driving position for an automatic
overdrive transaxle. It automatically upshifts or downshifts as
the vehicle speeds or slows.
However, D (Overdrive) also shifts into a fourth gear — an
overdrive gear — when your vehicle cruises at a consistent
speed for any length of time. This fourth gear will increase your
fuel economy when you travel at cruising speeds.
When to use D (Drive — with Transaxle Control Switch
activated)
D (Overdrive) may not be appropriate for certain terrain. If the
transaxle shifts back and forth between third and fourth gears
while you are driving on hilly roads or if your vehicle requires
additional power for climbing hills, depress the TCS. D (Drive)
also gives more engine braking to slow your vehicle on
downgrades than D (Overdrive).
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