The overdrive is engaged and disengaged based on the vehicle speed and throttle position.

At wide-open throttle, the system will 3-4 upshift at the wide-open throttle overdrive speed.

At closed throttle, the system will 4-3 downshift at the minimum overdrive speed.

For throttle positions between fully-closed and fully-open, the system calculates a proportional speed between the minimum and wide-open throttle parameter settings.

The drawing below illustrates the relationship between throttle, speed, and the overdrive parameters:

Minimum Overdrive Speed

This parameter adjusts the minimum speed at which the overdrive will engage.
This is also the approximate speed at which a closed-throttle 4-3 downshift will occur.

Wide Open Throttle Overdrive Speed

This parameter adjusts the speed at which the 3-4 shift occurs when the throttle is at 100% or fully-open.