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
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.