Old Jetta changed the front door and slowly controlled the rear window.

The reason is a circuit problem or a motor problem.

1. Circuit problem: If the front and rear window circuits are poorly connected or the circuits are aging, the vertical speed of the rear window may slow down. At this time, it is necessary to check whether the circuit connection is normal and whether the circuit elements need to be replaced.

2. Motor problem: If the motor of the rear window is aged or damaged, it will also slow down the vertical speed. The motor needs to be replaced at this time. Modifying the front door control rear window may affect the circuit and transmission system of the original car, so we should carefully choose the modification scheme to ensure that the modified circuit and transmission system are normal.