Which of the following is a part of the air leak check procedure?

The air leak check procedure is essential for ensuring the proper functioning of a vehicle's air brake system. Activating the service brake and holding it is a key step in this procedure because it helps to determine if there are any air leaks in the braking system. By applying the service brake and maintaining pressure, the operator can observe if the air pressure drops, indicating a possible leak within the system. This is crucial to ensure the brakes will operate effectively and safely under normal driving conditions.

Measuring air temperature in the cabin, adjusting pressure settings manually, and checking vehicle oil levels are not direct components of the air leak check procedure. These tasks pertain either to cabin comfort, general operational settings of the vehicle, or engine maintenance, rather than the integrity and functionality of the air brake system. Properly performing the air leak check is vital for vehicle safety, enhancing the overall reliability of the braking system.