When towing a vehicle, what must be disconnected to avoid damage?

When towing a vehicle, it is essential to disconnect the drivetrain components to prevent significant damage to the vehicle being towed. The drivetrain includes parts like the transmission, driveshaft, and differential, which are responsible for transferring power from the engine to the wheels. When a vehicle is towed with its wheels on the ground, the drivetrain components can rotate and be subjected to forces they are not designed to handle when the engine is off. This can lead to premature wear, overheating, or even catastrophic failure of the components.

For example, if a vehicle with an automatic transmission is towed without disconnecting the drivetrain, the transmission could suffer serious damage because it relies on the engine running to properly lubricate the moving parts. In contrast, the other options such as the steering column or braking system might not directly cause damage related to the towing itself, and while disconnecting the fuel line could have safety implications, it is not as directly related to preventing damage during towing. Understanding these aspects is crucial for safe and effective towing practices.