All of the following, except one, could cause the parking brakes to fail or not hold. Which is the exception?

Air in the brake system is typically associated with hydraulic brakes, which are not directly linked to the operation of parking brakes in most vehicles, as parking brakes often function mechanically rather than hydraulically. The presence of air in the brake fluid can affect the vehicle's ability to stop while driving, but it does not have a direct impact on the parking brake's ability to hold the vehicle stationary when engaged.

On the other hand, worn brake shoes, corroded cables, and improper adjustment can all directly impair the function of the parking brake. Worn brake shoes reduce the friction required to hold the vehicle, corroded cables can prevent proper engagement and release of the parking brake, and improper adjustment could lead to insufficient tension in the system, leading to ineffective braking. Therefore, air in the system stands out as the exception in this context.