What is a ptu on a ford escape?

The PTU on the Ford Escape is the power transfer unit. This unit transfers power from one of the rear axles to the other, without the need to share hydraulic fluid between the two systems. In short, this is part of the system that takes the rotation of the axle in the back of the vehicle and transfers the power to the front, allowing You to drive. If this unit is bad then You will likely not be able to move the vehicle, or if You do it will be severely underpowered. Do not try to drive like this, You will damage and brake the rear axle, turning a moderate repair bill into a large repair bill.