Ford Mercury Villager 1997 Owner's Manual page 227

Driving
Driving
When to use D (Overdrive)
Overdrive is the normal driving position. When the gearshift
lever is placed in (D) Overdrive, and the Overdrive Off button has
not been pressed, the vehicle will automatically upshift to
second, third and fourth gears. The transaxle will shift into the
correct gear when the right speed is reached.
When to use D (Drive — with the Overdrive Off button
activated)
You will notice that there is only one drive position on your
gearshift selection indicator (instead of Drive and Overdrive). You
will find a button labeled OVERDRIVE OFF/ON located on
the gearshift lever. Push in the button on the end of the lever and
the O/D OFF light in the instrument cluster will illuminate.
With the O/D OFF light illuminated, the transaxle will operate in
first, second and third gears and will not shift into fourth gear.
Operating in Drive (O/D OFF) provides more engine braking than
Overdrive for descending hills, or city driving.
The OVERDRIVE OFF/ON button
To return the transaxle to the normal Overdrive operation,
press the OVERDRIVE OFF/ON button again. Use this button to
select Overdrive or Overdrive Off whenever you drive your
vehicle.
NOTE: Overdrive will not engage until the engine has fully
warmed up.
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