Before coupling, what must be inspected on the tractor?

Before coupling, it's essential to inspect the alignment of the fifth wheel. The fifth wheel is a critical component that connects the tractor to the trailer, enabling the transfer of weight and facilitating safe towing. Proper alignment ensures that the trailer is securely and correctly positioned on the fifth wheel. If the fifth wheel is misaligned, it can lead to difficulties in coupling or result in dangerous driving conditions once on the road, such as swaying or detachment of the trailer.

Checking the engine oil level, operational condition of mirrors, or cargo capacity of the trailer, while important parts of overall vehicle maintenance, do not specifically pertain to the immediate process of coupling. These checks are more relevant to ensuring the vehicle operates correctly during travel or in a broader scope of safety checks. Hence, aligning the fifth wheel is the most critical step right before coupling.