The control of the automatic transmission unit in the Volkswagen Passat B5 is located inside the engine control unit (ECU).
The exact location depends on the ECU model, but it is usually located:
* In the engine compartment, often next to the battery.
*Under the instrument panel on the driver’s side.
* In the fuse box inside the car.
To determine the exact location, consult your specific vehicle’s owner’s manual or use online resources such as a vehicle diagram.