What is one critical inspection when coupling a tractor to a semi-trailer?

When coupling a tractor to a semi-trailer, one of the most critical inspections is ensuring that the fifth wheel slide is locked. The fifth wheel is a vital component in the coupling system, responsible for securely connecting the tractor to the semi-trailer. If the fifth wheel slide is not locked, there is a risk that the trailer may disengage from the tractor while in motion, which could lead to severe accidents and loss of control.

Properly locking the fifth wheel ensures that the connection is stable and that the tractor can safely pull the trailer. This step is essential for maintaining the integrity of the coupling and ensuring that all weight and force are appropriately distributed during travel.

The other options, while important for overall vehicle maintenance and safety, do not directly pertain to the immediate and critical coupling process. Checking engine oil levels and brake fluid levels are essential for the vehicle's operation, but they do not affect the security of the connection. Ensuring the fifth wheel jaws are open is also necessary, but that is a preliminary step before making the connection. Thus, verifying that the fifth wheel slide is locked is a crucial step that directly impacts the safety and functionality of the coupling process.