Why would a power window go down but not up on a Pontiac transport?

A power window that goes down but not up in a Pontiac Transport could indicate a problem with the window motor or the regulator, as these components are responsible for the window's movement in both directions. It may also be caused by a faulty switch or wiring issue, preventing the up command from reaching the motor. Another possibility is a blown fuse related to the window's power supply. Diagnosing the issue would require checking these components systematically.